this is mostly due to the very basic AI pathing of raiders, deathclaws, and feral ghouls. I do not build a second column of elevators. it's not a good idea to have a level that only has a mr handy on it because they are only really effective at stopping the spread of incidents and that's only if they are patrolling that room when the incident occurs

Mr handies are best used on levels that have consistently empty rooms as these are most likely to get infestations/incidents that spread if you don't get dwellers to them fast enough. using this layout, any infestations can easily be responded to, quickly since each level has dwellers an equal distance away from the outer-most edges. unless your vault is overpopulated, these are usually empty during active play anyway, and best used when you're getting ready to sign off. To the right of the production rooms, this is typically where I build the rooms that are fixed double-wides, like the overseer's office and barber shop, as well as the training rooms.

any rooms that typically remain empty go to the left of the elevators, for the most part, this is typically the storage rooms, living quarters, radio station, and workshops. this places the vast majority of dwellers in the center of each level.

My optimal plan has been to locate all triple wide production type rooms immediately to the right of these elevators. (with the option of a second column of elevators somewhere in this right portion. using this default elevator placement allows building 3 rooms to the left of each elevator, and 5 rooms to the right. the default layout is 3 levels of elevators immediately in front of the vault door. So I'm sure most of you know there is space for 8 rooms and 2 elevators per level. So I've been playing around with vault layouts and I think I've come across the best layout for efficient use of space, rapid response during incidents, the fewest dead dwellers, and the best use of mr handies.

Fallout shelter room layout