We did some testing a few years ago to see how high we could go with sidedress applications of nh3 and 32%.

in the case of 32% it’s mostly limited to the capacity of the equipment, but we ran up to 210 units /acre before we ran out of capacity.
In the case of nh3 it appears we can do about 230 units/acre before we just can’t seal it up anymore, 170 units seems to be the practical limit.

Top dress urea is pretty rare here, but last year there were a couple different operations that did a fair number of acres of top dress, I think they were running 150 units.
The combination of high temps and poor soil moisture conditions combined to make some fairly ugly looking corn for a couple weeks. It’ll be interesting to see if they try it again this year.