After a week of tuning this is what I found.
Moving from T-Factors to new Vapor,
Part 1: with one foot in each boot and your feet positioned at the same distance from a wall the measuring point difference (back of rubber vs back of hard shell) is 3/8" with the Radar being further forward.
Part 2: The radar boot when positioned as far forward as allowed with factory mounting features allow, your foot position ends up 1/8" back of T-Factor when TF is mounted in the neutral position (center hole).
To compensate for this, shift the mounting features for the hard shell forward about 1/2" on the plate. (easy if you have 2 plates, just screw them together using the center mounting holes and spot new holes)
So if your making a switch while you can measure off the heal of the shell you still need to compensate for where your foot really is on the ski.