What will you do with just dwarves? They'll only reflect spells, and you'll just ignore the rest?
To understand what and how, read Fizmig; you'll find out everything there.

I didn't say anything about dwarves; you're just imagining things. Read my previous post again.
Thorgrim, at level 20, reflects every other spell, provided he's an expert in magic resistance (which is inevitable), targeting any creature in his army. If you cast on dwarves, it's useless because the chance of success is around 10%. Try casting a mass slow spell on Thorgrim, level 20, and you'll see that the spell won't affect all units.
I read the hero physics section carefully. It's a detailed work, but it only contains factual information about who hits whom; there's no information about how.