Front wall speaker distance

You must not have read my answer. I recommend that you do.

Not the back.

Driver side since its distance is what determines the time delay between direct sound and the first reflections which in turn indicates things like frequency of the SBIR null (where the driver is 1/4 wavelength from the wall thus making its first reflection 180 degrees out of phase).

It does not really matter because you will place the speakers where they sound best. Just make sure you using the same procedure for each speaker. IOW's if both are 24" measured to the front of the speaker cabinet where the tweeter is located does it really matter that they will also have equal measurements to the back of the cabinet??? Measurements are just that, pick a point and start there, be consistent and put tape on the floor so you can recreate positions that sound good and compare them. Subtle tweaking will be required for best sound. Put the spikes in after you find the sweet spot.