[PhilD]

I didn't check the manual (I would if I had it as a searchable PDF file), but I seem to remember that difficulty depends on the dispeller's penetration, and a comparison of how many extra gems are used by both the dispeller and the original ritual. If this is correct, then using a site with a ritual bonus is effectively useless when using extra gems, because you need extra gems over the "normal" cost of the spell to get the benefit.