Are there different versions of pivot bins on these planes?

On a recent 739 flight I'm pretty sure the pivot-bins only allow for horizontal bag storage (i.e. no more bags than a conventional bin). However I think I can remember other UA aircraft with bags turning onto their side (i.e. "50%" more bags per bin). Am I going crazy or not?

(I must say, the slimlines on these planes don't fit my body at all - the headrest protrudes too much so I can't sit comfortably at all. Admittedly they are softer than the A320 Recaros, but the Recaros have more than enough padding for me already.)