Did you try sending them back for a refit? Usually you get a refit free of charge and should solve some of your isolation issues.

Buying the X4 was a very bad decision for me, the don’t feel great, in fact they are a bit uncomfortable, the one on the right side does not feel that well. Also, they sound great by themselves, in the studio but playing live they let so much of the sound pa bleed in that it is unbearable, so I would say if you want to use them for studio work or listening with them to a movie on a flight they are perfect but for live performing no way, my Shure 535s sound 10x better and they isolate 100% better. $1000 went down the drain

I have not done a sit down comparison so this is from aural memory of the two but I would say the U4s is a little more exaggerated on the bass and with a more pronounced V-shape.