Seems that the number of modifiers is calculated incorrectly (in the createMobModifiers method).
In the current code, there will only be 2-4 mods for eliteRarity chance, 5-8 mods for ultraRarity chance, and 8-12 mods for infernoRarity chance.

And what, the readme says something different? You don't like that 8 can be a result of ultra and inferno both? What is wrong with it?

So the calculation for drops does not match the modifier calculation? That's possible i guess. To match the upper logic:

int prefix = (modStr < 5) ? 0 : (modStr < 9) ? 1 : 2;

But really, it should have been a common constant instead of these magic numbers.

Uhh sorry I did not describe the issue clear enough... I'll edit the first post as well.
I took a peek at the code and I think the intended mod number for each tier is shown by these few lines:

    private void dropRandomEnchantedItems(EntityLivingBase mob, MobModifier mods)
    {
        int modStr = mods.getModSize();
        /* 0 for elite, 1 for ultra, 2 for infernal */
        int prefix = (modStr <= 5) ? 0 : (modStr <= 10) ? 1 : 2;

So the intended numbers are 5- for elite, 6 - 10 for ultra, and 11+ for infernal.
However in the createMobModifiers method the resulting number of mods is less than intended.