Night Fishing Question

I've been catching some nice ones during the day, 30ft. + brushpiles, but the heat is a killer. I tried night fishing for the first time last night, pulled up to the brush, put out anchors and lights. We caught about 45 little crappie in 3 hours, then the stripes moved in. Used 6 Doz. Minnows only 3 keepers. Where did all the BIG CRAPPIE go? They are there during the day why aren't they there at night? Do I need to fish farther out from the boat? Any help would be appreciated.