Don't most broad heads come with these instructions on the box? I know some of the ones I have bought did. I would also suggest shooting the hunting tipped arrow first, and then the field point. Unless you like slicing vanes and arrows in half when you start to get close. I have sliced a carbon arrow in half from nock to tip doing this. It gets expensive, shooting the fixed blade first works better.
Also keep in mind, just like paper tuning or bare shaft tuning you may have to do the opposite to get what you want. Depends on the type of release you have and the spine of your arrows.
And who said tuning your fixed blades to hit with your field points is the best tune for your bow? You may actually be detuning the bow in order to get them to do it. It's convenient, but is it really the BEST tune? Some say no.
I would be more concerned with how the arrows fly and group then I would if they hit the same spot. If you can get both, that is great. However I have seen tuning for this actually opens up your groups a little and effects the flight of the arrow some.
Just stirring the pot for you
Paul