More bottom lip in the mouthpiece isn’t necessarily a problem as you go higher. I’ve been having that sensation a bit lately while doing some pretty effortless-feeling harmonic slurs above the staff. The aperture has to be reduced as we go higher and the lips should contract towards the center of the mouthpiece /air column (my understanding…). As long as you’re not rolling the bottom lip under the top lip or engaging the lip muscles too much / clamping, then your bottom lip moving in might not be a bad thing. If it feels and sounds resonant and efficient, it could be ok. My $.02 FWIW, correct me if I’m wrong. Good luck!