@Bill, from my understanding the way the trap is designed you want the fish to turn left or right once 2/3 of the fishes body is beyond mesh furthest inlet. Giving fish too much room after they have entered the trap allows fish to turn toward exits and possibly leave. Fish tend to pass exits if there is little room for them to try and make a 90 degree turn. My case we are trying to get 2"-6" fish out meaning I have my bait tube about 3" from the openings, forcing fish to turn.
If I pushed open the entrances a .25" and made my bait tube slightly smaller I'm sure I could get 6"-8" fish in it easily. On that note I would imagine I lose most of 2"-3" fish.
This pond was stocked only with HBG. We had 5 straight years of only seeing HBG caught. Another pond on our property above this one had a major rain event, even with ruble and fish netting managed to get at least a few pure bluegill in the HBG pond. This past year I'm starting to see more characteristics of BG mix in our HBG population. So we are trapping small - medium sized fish giving them the eye test more HBG the go back more BG traits they get used as bait. Three months ago we also stocked 300 pure greenies to help get those desired traits back in line.

Forced to work born to Fish