Eternal Youth and Recoup

So if i have '10% damage taken recouped as life', and take 1000 damage with 700 es, of the 300 damage i actually take i recoup 100 over 4 seconds?

because it sure seems like im not recouping anything. is it treated as regeneration and being put on my es?

Recoup and Regeneration both are subsets of Recovery. Eternal Youth should have no effect on Recoup. 10% over 4 seconds likely won't be very noticeable. That's only 2.5% per second. You'd have to test it with 0 other sources of Recovery active.