Arrow length can be governed by several things, but to get to where you can answer this question, you will need to become proficient in tuning your bow and shaft to each other. You will need to understand the different shaft spines and how your bow reacts to them. Shooting style can also effect shaft length, for instants, gap shooter sometimes like a longer shaft, to give them a smaller gap.
There are so many elements to the equation that only YOU can determine what that correct length is.
Start by learning to tune bare shafted. Start off with a full length bare shaft say with 100 grain tip. Glue the insert in with some hot melt glue from Big Jim's website so you can easily remove the insert with a little heat, to cut the shaft when needed. He has a video on his website that explains how to do it.
Once your shaft starts flying straight, you know you’re in the ball park, and you can then make the decision whether you want long shafts or short shafts. If where you end up is several inches past your draw length, you know you have more room to cut the shaft for heavier tips. A good rule of thumb to remember is, long shaft light tip, short shaft heavy tip.
If you go through the bare shaft exercise, you will get it. It's kind of like juggling three balls. As a matter of fact it's exactly like juggling three balls. You got to juggle shaft length, with tip weight, with brace height.
PM me if you need more help.
Good luck!