WHOA... so you only need to consume another ToC after you collect your stash of exotic engram drops... so you can pop one... kill him over and over and amass a stack of engrams... then collect and only need to pop another ToC after you do so?!? Yeah... shit will be patched soon!! lol
No. Your consumable is used when you kill the guy. But let's say he dropped an Exotic. You leave it on the floor, use another Coin...and it will trigger the "stack" thinking your previous kill didn't give you an exotic.
So you're still using one coin per kill, but by not picking them up you're fooling the game into making each Coin raise the probability for a drop "because last one didn't work".
Interesting theory, but it's just confirmation bias until more people report a better-than-1/5 chance using this method.