I do the same thing, only I align my cock feather over the stiffest axis of the shaft.
This was a dilemma that I had. I first went through the group and tested 4 sides on each arrow and noted what they were. When done I found a few that had 3 similar sides and one weaker one. The were a couple that had 3 similar sides and one stronger one. I could have gone either way. I also wondered if it would be best the find a side that was the same on all arrows. For instance, if most arrows had one side that tested .330, maybe it would be best to put the cock feather on a spine that was the same on each arrow, regardless of whether it was weak or strong compared to the other sides. Down the road, I hope to try that on a dozen to see what the results are.