Neil,
Welcome to the forum!
If you post a picture or two of your bracing, some of us could answer a little better.
What size are you building?
How thick is your top and how tall and wide are your braces?
Think about removing width, not just height from the braces. Make the braces narrower towards their top. That removes mass to let the top move without reducing a lot of stiffness. Remember, stiffness is increased much more with height than width of the brace.
Be very careful not to run the chisel into the top.
You'll want to cap the X-brace joint with a thin (.05") piece of brace material and think about tapering the x braces on lower bought to the top rather than in-letting them into the rims.
Keep carving until the tap tone is pleasing and musical to you, but the key is knowing not to go too far. That comes with experience, but you probably do not want to be much less than 9/16" at the X and that should be your highest point. If you get to the point where the top sounds dull and muddy, you've gone too far. That is the point when you'll know if you have gone too far. You want to get close to that.
If you have the time and material, you might want to keep carving and listen while you go too far on purpose. Then remove the braces, and put new ones back on, and start carving again, but this time, stop short of going too far. If you do that, you'll be way ahead of the game.
Remember, this is just my opinion based on my experience.
No warranty/guaranty etc.
I think it should give you a good start.