Alf,
I take it you have a fairly recent BR, like me (October 2009). On these more recent boats I feel the mainsail is cut with more belly, and I too have trouble with some wrinkles despite having a stiffer topmast.
However, a stiffer topmast helps a lot. But there it is not primarily the carbon content that counts, but the IMCS (Or ICMS, I forgot) coding of the mast, which is the stiffness indicator. The higher the IMCS is, the better. A IMCS of 32 minimum is OK.
You can build your own topmast, its simple. Best stragegy is to buy a very long windsurfer mast with high IMCS, and shorten that, which brings the absolute stiffness up further.
Good luck.