My diffuser is 4' off the bottom, so 12' from the surface when the pond is full.
Right now the pond is down ~2', which puts the diffuser 10' from the surface.
If I were going to speculate on the smaller temp delta between the surface and the depth during extreme hot weather
I might think that is due to the relative volume of warmer surface water compared to the cooler water in the deep sump.
So I'm pretty sure the answer is "it depends". lol
