Just shoot as far back as you can and be safe.Being farther back than your hunting shots just helps confirm that your tuning is really on the money.You don't have to have super tight groups,you just shoot a lot and average the results you are seeing.If your bare shafts are grouping with the fletched,at say 25 yds,and ultimately later,your broadheads do the same,you are there,regardless of your group size.
I often refer back to OL's tuning information.It has helped me a lot.I follow it to the letter.I generally start tuning at 15 yds and as I see it coming together,I move back and eventually get to 30 yds.When I get to where I have confidence in shooting the broadheads at that distance,I am done.Then I can go back to working on me.
I also like to keep my hunting shots 20 yds and under but tuning farther just gets them dialed in.A well tuned arrow will penetrate better and be most forgiving of release or other form errors.
Good luck with your tuning.Once you have a setup tuned,the next one will be much easier.