I don’t think this is a stupid question I think it’s an excellent one. I’d also roll my eyes at anyone saying you need to bump some water parameter up or down a tiny bit - the fact is that these corals thrive in a variety of water parameters and yours look fine to me. I have some Euphyllia in a very new tank and it’s doing great, the whole “tank not mature” enough thing is nonsense - as long as your parameters are reasonable and stable, I don’t know what “maturity” has to do with anything.
Anyway - I agree with the comments on lighting and flow. I have found that mail order corals don’t do so great with higher/whiter lighting. I had to turn my flow and lighting way down (and less white) to make new arrivals happy. I think this is a strong possibility especially if you have only one other type of coral and it’s fine - it’s probably more lighting/flow tolerant. My 2cents, good luck!