HP to weapon/magic def ratio?

I was wondering how much weapon/magic def is equivalent to in hp is there a formula I can follow?

 

if it helps, with max magic def (1999) shao still hit 11600 on my bish... so based on this anecdote maybe 5mdef = 1hp?

 

its something like monster base att -your def
but i have no idea how monster base attack translates into damage

 

I got a different question about this.
Does Weapon def only protect from touch damage and Magic def protects from long range attacks?
Or does magic def protect from magic attacks only, so, if I wasnt hit by an attack that had magic in it, even if it was long range, it'd hurt me based on my weapon def?
Because as Bishop I have like 1400 m.def, but I think I still get hit pretty hard by magic attacks. And apparently, the more INT I have, the more magic def it gives.