Not sure if you've purchased the case yet, but if you haven't, then wait for the release of the MkIII coming out in early Q3 according to Louqe. Wasn't aware of an upcoming release when I'd purchased mine earlier this year. So suffering from FOMO right now XD.
So, when comparing the asus X570 itx against their b550 itx, I noticed a few things:
B550 and X570 appear to use the same VRM description, but visually the layout is different
X570 has waaaaaaaaaaayyyyyyyyyy more rear I/O
B550 has higher max memory frequency
(sources used: Asus X570 ITX...
Did your temps improve upon reverting to air cooling? By any chance did you happen to try getting temp readings with the rad/fan in open air and not mounted in the case? Any difference if the fan is set to pull instead of push?