Changing battlemat scale from 1 square = 5' to 3 squares = 10'

This has several advantages in terms of plausibility, mobility, et al.
Base sizes stay the same, so a 1" base figure still occupies 1 square, now about 3.3', or 1 meter. For diagonals, count 1 diagonal as 1 (3.3'), 2 diagonals as 3 (10').
5' reach = 2 squares
10' reach = 3 squares
15' reach = 5 squares
20' range = 6 squares
30' range = 9 squares
Now 8 characters with 5' reach can attack 1 from adjacent squares as before, but an additional 3x4=12 can attack from the second rank, the target benefitting from cover (+2 AC). Still, a mob becomes a lot scarier without having to worry about any in-and-out dance!