V&F is basing agnostic. Designed for 28mm, all you need do for smaller figures scales is adjust ranges and movement distances. I use 15mm, so 2/3 distance works for me, easy since almost everything is a multiple of 3. The real determining factor is the frontage of your units. The 28mm figures in the rules have a frontage of about 7 inches. My 15mm units have a frontage of 4 inches. If you have loads of smaller figures per unit and your frontage is 6 inches or so, use the written distances. Smaller? Reduce them.