The OP said "shorter" not "smaller" and the BA spec of 4.5x18.5" is cylindrical so the volume should be 294 ci (~5 liters). The Kelty shows a rectangular packed shape in on its site, but without the third depth dimension - my guess is that it's 11x14x3or4" which is 462 or 616 ci (~7.5-10 liters). While the interior floor space is about the same, the BA vestibule is 8 sf, vs the Kelty at 20 sf (2x10) and a lot more useable, and clearly the headroom is better.

If you want to pack a tent as one piece, it is always better to keep the weight low in a pannier, with the less dense sleeping bag up higher on the rack (assume dry bag). But that said, the 18.5" of the BA are obviously the poles, so you can always separate just the poles for the top of the rack. Then again, I personally like everything tucked away into a bag for cleaner appearance, less fiddling/items, and quicker, easier on/off.

IMHO, the Kelty will be a lot more comfortable if holed up for a day or two in bad weather, but I do agree with others that there's a big weight/volume penalty for that. For perspective of the other extreme end of the spectrum, there're ultra-lighters like me who's entire "house" (tent, sleeping bag, pad, kitchen) is ~5lb/10L and it all packs into a single pannier, even adding another 12lbs of clothing, gadgets, food, and water. But I'm a just a short tourer typically out a week or less, whereas the OP sounds like he'll be nearly living out of his rig for an extended period of time.

Tough call, we all have our own priorities... good luck in your decision.