In the plush world of bed-filled business-class cabins, seating isn't about aisle, window and middle. Instead, it's herringbone, V-shaped, staggered and even 'yin yang.'

The airline industry, usually cookie-cutter and copycat, has struggled to find the optimal layout design for fancy cabins in the front of planes flying international routes, where tickets often cost $5,000 to $10,000 or require paying for upgrades with cash or points or both. That is largely because passenger expectations for business-class comfort and convenience have increased, and that means more square footage for each seat. Seats that turn into horizontal flat beds usually mean abandoning traditional straight rows, for example, since passengers' feet can no longer slide up under the seat in front.

And now the newest premium perk -- direct aisle access from every seat -- is leading to more floor-plan inventiveness and experimentation. To keep one flier from climbing over another sleeping passenger to get to the bathroom, airlines are angling and staggering seats in new ways.

'We seem to be in quite an ingenious race to find new ways to overlap people and interlock people,' said Peter Tennent, director at Factorydesign, a London firm that has worked on seating issues for several airlines and seat manufacturers.

Delta Air Lines has three different layouts in its business-class cabins for international trips. Older seats are lined up straight but newer seats are arranged in either an angled herringbone pattern or staggered. Both of those designs give every passenger direct access to aisles, a perk Delta says it will have in its entire international fleet by summer 2014. The airline says it prefers the herringbone design, with feet pointed toward windows. But it found that in the Boeing 767 fuselage, which is narrower than Boeing 777 and 747 planes, a staggered layout accommodated more seats than angling them.

'At the end of the day, the question is how do you maximize revenue per square foot,' said Don Cox, Delta's director of customer service.

Old-style business-class seats, still in use at many airlines, line up in straight rows and flatten out at an angle for sleeping so one passenger's feet slide in below the passenger's head in front. The downside: Sleeping passengers might slide down in the seat because of the angle, and the window-seat passenger has to climb over a sleeping traveler to get to the bathroom.

So airlines are increasingly rolling out horizontal flat beds that are more conducive to sleep. On Wednesday, American Airlines announced it will retrofit its international fleet with beds that lie fully flat and provide all-aisle access over several years. The new layout will give passengers on American's Boeing 777s twice the 'living space' as they currently get in business class on those planes.

But horizontal beds take up more space since one passenger can't angle under another, and airlines end up with fewer premium seats to sell. On most planes, the difference is often only a handful of seats, but it can be a lot more. American decided to reclaim some space on some of its 777s by eliminating first-class cabins. For Delta, which eliminated international first class years ago, the new herringbone layout yields 48 business-class seats on the Boeing 747, 17 fewer in the same amount of space as the older design, which didn't have horizontal flat beds and direct aisle access for every passenger.

Delta and other airlines are betting that less will be more in terms of revenue. By making the seats more attractive, airlines think they can win over customers from other airlines that don't have the same perks, avoid some discounts on business-class fares, or at least prevent fliers from abandoning them for competitors that have upgraded. Bottom line: The hope is new cabins will generate the same revenue, if not more, with fewer seats.

'You have to make up for it with increased customer preference,' said Delta's Mr. Cox.

British Airways dealt with the problem of what to do with feet when you go to horizontal flat beds by placing seats next to each other facing in opposite directions -- what it calls yin yang. Since people are wider at the shoulder than at the feet, the seats taper, and one passenger's feet end up on the other side of a partition from a seatmate's head when both are sleeping. Half the cabin flies backward (actually a safer position to be in for a crash landing).

Yin yang seating packs in travelers more densely than herringbone and staggered designs, British Airways contends. But yin yang doesn't allow direct aisle access for window-seat and middle-seat passengers. British Airways, which has a patent on the yin yang pattern, doesn't think direct aisle access is a major issue for most travelers, said Simon Talling-Smith, BA's executive vice president for the Americas.

'We know the No. 1 requirement -- absolute No. 1 -- is sleep. Nothing trumps sleep,' Mr. Talling-Smith said.

Singapore Airlines says its research finds the same conclusion: The ability to sleep is what sells business-class beds. But most business-class beds aren't wide enough for deep sleep because passengers can't change positions without waking up. So Singapore reduced the number of seats in each aisle of business class and installed seats more than 30 inches wide, up from 27 inches. Each passenger got direct aisle access, something Singapore, like Delta, found travelers really do value.

'It is still evolving, and it's always going to evolve,' said Singapore spokesman James Boyd.

One idea seat manufacturers have been showing airlines: horizontal flat beds that stack vertically, perhaps like bunks on a train. So far, there have been no airline takers.

Mr. Tennent, the designer, says he doesn't think the industry will ever settle on a single solution. Different airlines have different priorities for passengers. 'Like any good recipe, it's got a lot of ingredients,' he said. 'I would challenge the notion that there is a dream layout out there that will satisfy everyone.'