Talking from nothing but seat of the pants/gut feeling...so beware of opinions offered below...however have sailed fractional
rigged boat for many years.
See if you can have a conversation with your designer
or if not
Fractional rig main has much longer foot than masthead rig.
Fractional rig has mast positioned forward of masthead rig
and with swept back spreaders.
Center of effort vs Center of lateral resistance changes, which
will effect balance of helm
Seems that you would be making a tall rig version, not fractional rig.
You might want to explore a new boom and mainsail
longer foot (and larger roach as suggested by Bash) my
30' fractional rig main has a foot of 13', this is larger than
usual masthead main, about the size of a 34-35' boat.
But this is serious design territory, not to be done without
proper designer scrutiny.
My suggestion if proved out before hand is to explore larger
foot and roach on main with current
mast height and see what
that does to reduce headsail to 100 % you were looking for.
Does your boat currently have weather/ lee helm tendencies?
Haven't even thought about engineering involved in extending
We have an accomplished designer who is a member
of the forum, perhaps around he might weigh in.