BC or trim device i prefer calling, can be adjusted to sit lower.backplate alu? adjust and lower the harness on the shoulder and compensate/shorten the crotch strap.you could well repositioned the entire trim device lower by up to 4-6cm.
It's good advise donning full wet suit as well with 5mm bootie or more.adding a weight to tank nearer to top would balance up perhaps.also try to position the tank higher as high as ur head,thus shifting weight balance.check also ur accessories well balanced on both sides.i have experimented bungee the higher bladders so as to direct more air inflation towards the lower end of the BC.it's up to ur discretion to try this if it is last resort without changing out JF.
the trick is weighting and with counter balance, tuck tightly the hips/glutes and a zero-movement hoover can be rediscovered.
Feeling weightless and 'floating' in the depths is the correct sensation to begin with, that indicates correct weighting for the best trim dive that will follow with correct posture and finnings.