well thats an old problem many many bow hunters have had
many broadheads fly differently than target tips
BUT many times its not the heads, it the bow out of tune
some simple fixes
well lining up the blades with the fletching
Paper tuning your bow with broadheads
or like so many have done, go to a GOOD expandable broadhead
there are many good one's out there now a days, that almost are fail proof to NOT open
But a fixed head will always have an advantage in reliability, BUT only if they fly where you want them
so I suggest you start with paopertuning and turning the heads to line up
if that doesn't solve the problem
you can try weighing the heads, and spin them to see if any are out of straight, that can happen on them, causing them to fly true too
same as the inserts in the shafts too, if there not in straight
could be lots of small things that add up
but starting with paper tuning can be a BIG help
smaller shorter head always seem to fly better out of faster bows too
as size of blade/head can effect flight with speeds
also could be your arrows shaft size?
a broad head will have more resistance than a target tip of same weight and can cause a shaft to flex more
just some off the top of my head
But I went to rage heads and fly perfect for me, if I do my part
but an out of tune bow will be an out of tune bow no matter the head
just some can get away with target tip/expandables better, than with a fixed head!
good luck