Thanks. This issue is twofold:
a) it is rounding the numbers in the panel. It actually has 3.06 damage, it just appears as 3.1 because it rounds.
b) It also rounds all values to 2 decimals in the damage formula, so it can happen that some end values for some units differ slightly from the values we feed into the calculation. Sadly we cannot change it to having a flat 3.0 on level 3 with the current setup, without also changing other damage values (i.e. defense vs soft targets) on level 3.