My OME HD Install experience

I purchased the 3" OME HD lift from Kolak and it delivered as promised. I will go into the full install in a build that I am making but I wanted to post the numbers, Front both sides were at 18" (Not bad) rear drivers side was at 19" but the Rear passenger was at 18" (this will become obvious later as well). The post OME HD install numbers were 21" all around except for that darn passenger side rear. I first installed the B spring on the RR and it sat at only 20 1/2. Then I swapped the springs and got it to sit at 20 5/8s (a little better). I do not know what is up with this Passenger side rear. Does anyone else have any probable explanations for this. The truck is at a full tank (not freshly full the line has started moving but is still on full). Any input would be greatly appreciated, but overall a fantastic lift, but I would like to know why its like this.