Well tbh, I believe FSs already have some of the best/most useful positional SAs to begin with...at least for Coverage based ones. Personally, I prefer Bonus SAs to be geared towards lNTs or Blitzing, vs. FF...as FS are generally forced to build in that direction anyways because of Coverage Schemes (FF more the realm of SSs). The Tackling & Strength needed to make FF SAs viable, also would have to be considerably high and would probably take you to the end build before you would really benefit much from it too. Zone Specialist Archetypes for FS does not lend itself well to building that way either. Just IMO.
btw Cactus...I'm one of your "SS Mateys" on Rumrunners!
