most people cant even get near 8% on a arrow tith a broadhead because no manufacturer has made them light enough to get less than 10% on the front.
With all due respect, that's a bunch of hooey. You have to make informed choices on how you make up and arrow and what weight broadhead you choose or you can get in big trouble when it comes to tuning and sighting in.
A 28" 2216 with 5" vanes and a 75 gn head will be around 6.3%. A Beman ICSH 340 with a 75 gn head and 4" vanes - not an unusual arrow at all - FOC's at a mere 7.2%
In both cases, going to 100 gn heads and 4" feathers puts FOC over 11%, making for much more stable and better hunting arrows.