Dave probably has the best feel for your situation down there, but a few thoughts from me.
You have the right idea about making surface area smaller so evaporation amount will be reduced in ratio to size. If you make the pond deeper, you could put the overburden around the edges and make it smaller, so you have less surface area. Drawbacks would be steeper sides that may not be mowable when the pond goes down.
If you go deeper, that then should be compacted. The ability to do this depends. If you go deeper, will it fill with water as you work. Sounds like you have good clay, the water shouldn't be flowing into it while you work. But if the water does flow into it, then you have to deal with how to fix that problem.
If you dig, do you have a way to haul and move that dirt?
I think this is why Dave was wondering if you could just raise water level to accomplish the same thing as digging.
Dave, what about Otto? ( I know, Texas is big
.)
