Fish size compared to water depth

[Bass Assault]

I fished the beginning of the month with several friends of mine at lake Amistad (Del Rio TX). The group that I fished with was mainly catching fish in the 8-15 foot range. The largest of the fish caught in this group was 2 1/2 lbs. at the most. We were all TX rigging 7 inch worms or lizards. Water temp was 57-59 degrees.

The other group was fishing the same sort of rigs/baits in 20-25 foot of water and caught about half as many fish as we did but they also caught 3 of the bigger fish (several 3 lbrs and a 5 1/2 lb.).

My question is geared towards this scenario. What would be the relation (if any) to fish size and the water depth? Is there anything scientific to this? If so, is it particular to the time of year (pre/post spawn)?

I've done a little research and found just as many huge bass (12 + lbs) caught in 3-4 foot of water as I have in 40 + foot of water. Just curious what some of ya'lls experience/opinions are on this. Thanks a lot.