I would bet that at least part of the problem is that you're holding the two instruments differently (which wouldn't be surprising, given the difference in their body measurements). In my experience the biggest problems people have with barre chords are not a function of finger strength; they actually stem from the position of the wrist. If you want to play barre chords easily, your wrist (on your fretting hand) has to be pretty straight. If it's cocked inward, it becomes much more difficult to make a barre, and to hold it. People often hold the guitar neck too low, whether they're sitting down or standing up using a strap. It helps with those "thumb over" grabs, but it doesn't do much for your ability to play barre chords; you really need to keep the guitar neck at a suitable elevated position to play a barre comfortably.

I often tell students, or people that I'm coaching, that the ergonomics of playing guitar are very important, and involve more than your fingers. Hope this helps.