We dont have a lot of largemouth over here on the east side. I have noticed that the smallmouth act simmilar to what you have described. It seems the larger bass hang out under the small fish and wait for easier larger pieces of food to fall. If you can get a jig or crank bait to them before a small one grabs it then you might get a couple of bigger fish. I'm guessing that the larger fish you have caugth are because you made it past the barage of smaller aggressive fish.

Its to bad we cant fish live bait fish here in WA. In Michigan it was fun to catch some little 3" to 4" sunfish or bluegill and put single hook right throught the back and hang them down about 3' to 4' below a big red an white bobber. Some times you get somem big bass that you could put both of your fists in the mouth. Some times you rope into a big ass pike or channel cat.