. I wouldn’t say that there is no science behind it to be honest. There certainly are no rules, but there are definitely best practices that can at least lead you to a good starting point and beyond.
Keep both iems and the Beyers. Extra references are always welcome. The Beyers have quite a V curve signature meaning that the mid is scooped away. You iems might do something similar. Also check your tracks on your living room system, and if you have a car, that works really great as well.
a thing that you can read up on is mixing to pink noise. It’s not a method to get a completely solid mix, but it can really help to get an initial right balance of levels across your tracks. Great technique to use as a starting point and as a sanity check. Certainly when the references you’re listening on are not perfectly honest.
Hope that helps !