I have a 4 Greater Affix Mutilator Plate with +6 ranks to Blood Lance. That means the base is +4 with a 50% bonus to +6 from the greater affix. This means for each normal rank of masterworking, blood lance should increase by 5% of 4 or 4 x 0.05 = 0.2. Then at rank 4/8/12, hitting blood lance should increase by 25% of 4 or 4 x .25 = 1.
I have my mutilator plate at 8/12 masterwork and crit on blood lance one time. The total ranks of blood lance at this point should be:
6 + 0.2 + 0.2 + 0.2 + 1 + 0.2 + 0.2 + 0.2 = 8.2 ranks of Blood Lance.
However, it is still only giving me +7 ranks of Blood Lance.