I think this year has created issues that none of us are accustomed to. The heat level of your lake may have fish holding just above the thermocline over mid-laker deep holes during the daytime hours, venturing into shallower feeding water during the night. Maybe try fishing in the very early morning, or in the evening just an hour prior to and into the dark. Points that have breaklines and ledges jutting out into real deep water could hold fish during lower light times.
I don't think you are doing anything wrong. We are seeing water temps in the upper 70's here at home and crappies can be caught but none of the really decent fish that we know are available. The forage that crappies use right now will drive the crappies as to where and when they can be caught. Just understanding that the big crappies do things different from the smaller crappies in any given body of water. If you are seeing smaller fish, try up-sizing your bait/jig and search the water either above or below where the smaller are being caught. Shade on the water can be a huge factor during the daytime hours when it's hot. It's not unusual for us to find nothing along a tree trunk extending down into 30 feet of water on the side the sun is hitting while catching fish 180 degrees around the trunk off the shaded side. Even shade created on the water's surface in wide open, featureless, water has held fish for us instead of the sunlit side of the water. Shaded water might be two or three degrees cooler and could be where to forage find some relief from the hotter open water without shade.
As I mentioned early on, this years extraordinary weather extremes has put the fish in a whole new gear for us and I'd assume that this is the same just about everywhere. The fish still need to feed and I'd bet that the weather swings have put the forage in turmoil. Find the forage, figure out where and when the forage moves or isa located and sooner or later you'll figure out a system to catch the decent crappies.
