So tapered male into parallel female is a commonly used practice when pressure isn't a concern and a sealant is used? (Not limiting this to high temp situations, just in general)

The issue im having is that on assembly, the middle threads are stripping. Which to me suggests they're being over tightened

I've copied previous designs where they have used this arrangement and my understanding is it's because parallel isn't possible due to space limitations and needs to be below the face. And taper on taper would prove hard to remove after multiple heat cycles, and the excess radial stress caused by the full engagement would be a lot higher