My xenon pucks have 20W lamps. You may have the 10W variety, so adjust my answer accordingly.

I never looked at my puck light spacing until you asked this question. It appears that our installers (who did a nice job) centered the puck lights in the middle of each cabinet (both L-R and F-B). These are on 18, 21, 24, and 36 inch wide cabinets. Looking at the finished product, it is a pleasing effect to have the light sources centered below each cabinet door.

Dimensionally, our lights work out this way:
For a 24" and 18" cabinet combo, the puck spacing is:
(open side) 12/21/9 (range)

For a combo of 21", 36" and 24" cabinets:
(open side) 10.5/20/18/21/12 (corner lazy susan)

I think the important criteria for our installers was to center the pucks on the doors, which is what I would suggest. Hope this helps.