I think the suggestion in the book was for 10 yard squares on a grid, when engaging in mecha scale combat. Most grids are 1 inch squares.

Regardless, in mecha scale combat you never need to know the size of something smaller than 5 yards. The shortest range increment is 5 yards... so I'd have 5 yards be basically equivalent to adjacent. I wouldn't try and create a system with sufficient granularity to represent 1 yard.

Given that, I'd just ad hoc 1 yard = 1 meter, and then say that 1 meter = 1 centimeter. This still gives a pretty long range for many things... a laser cannon will be able to hit a target at up to 300 cm away. You probably won't have a 10 foot long table... but engaging a target at that distance isn't really combat anyway, it's more like sniping.

I think that for medium distance, 40 cm isn't that bad.

If you want to play with smaller distances, I would reduce the granularity of everything 10m, and round all range increments up to the nearest 10. This requires changing only 4 stats, actually.

In a model with min distance = 10m, the longest scaled distance anything could be engaged at would be 150 cm, or 5 ft.