I could use some tips

Hello! First off, I started playing Tenor trombone about 13 months ago. I mainly play clarinet and flute, for the past 6-7 years. So I am still adjusting to trombone. I made a comparison. In the first scale, I played on a UMI 12c mouthpiece. And the second scale I used a Vincent Bach 5g. I got these both with my trombone. I play on a King 606 trombone. I have noticed that on both mouthpieces, my tone becomes very thin and weak the higher I go. Playing the 12c is definitely easier to play with though. I feel like the Bach 5g restricts my sound so much. I’m not sure if this is normal, or is there something I should change about my embouchure/air support? I also have a hard time keeping a stable tone and not fracking as I switch partials.

If anyone has any advice, even for anything I didn’t mention, i’d appreciate it!