Unless the broadhead is so long as to look like a harpoon, the length will make no difference on a well tuned set up. Weight and proper tuning are the keys. Many people who bare shaft (myself included) like to have the bare shafts a hair weak, that is actually due to the compensation effect of the fletching on finished arrows, and doesn't really have anything to do with broadheads.
The most common problem with broadheads is to have them show/fly on the stiff side. That is usually due to arrows that were stiff in the first place, but the archer did not realize it just by shooting and tuning with field points. That's why I like bare shafting or broadhead tuning (same principle but the reverse of bare shafting).
In a properly tuned bow, a broadhead of the same weight as field points should fly to the same point of impact without issue.