It has more to do with your arrow than the bow. In order to get your field tipped arrows to hit the same as your fixed blade arrows you need to be pretty close on spine. If not you will play heck trying to get them close and will most likely actually throw your tune off trying to do it.

If you set your bow up and tune it with field points to the best of your ability, then shoot fixed blades and they are several inches off and fly funky you can try broad tuning. However when you do this if you have to move your rest or nocking point farther than what you know you should have to then you probably have a spine issue. Try messing with the draw weight of your bow to see if it changes.

If you simply can't group fixed blade arrows it may be an arrow issue. Like your arrows are warped or the nocks are off/bad or the inserts are not square and your heads do not spin true.

Fetching contact can cause it as well.

Me personally I don't try to get my fixed blades to hit exactly where my field points do. If they are within a few inches I am happy. As long as they still group well. I shoot my bow at targets WAY more than I actually hunt with it. And when I do hunt with it I take shots that are close.

I tune with bareshafts and like to get them to impact with my fletched arrows at least out to 20 yards, but I prefer 30 yards. If I can accomplish this I am fairly confident my bow is tuned pretty well for that arrow and my spine is pretty close as well. Now if I screw on a fixed blade head and I shoot an inch or two off the mark I'm not going to throw a fit or go re adjusting my bow. Especially if the broad head arrows still group well. I can either change my sights my sights when I hunt or just compensate for it. I am more concerned with how the arrow flies, not that two differently configured arrows impact in different spots.

Lots of fletching and FOC seems to help with this as well.

The best broad head tipped arrows I have shot were the Nitro Stingers that are tapered and have decent FOC from the get go. These were very easy to broad head tune, even though they were pretty stiff spine wise for my bow.

This is my view anyway, many do not agree with it. To each his own I guess.

Paul