Admittedly my system for this power isn't optimal but...
I use the Extraction (pet) power to target a corpse (it always targets a dead one) then immediately use whatever key I have Unchain essence on.
It's a 2 button process but it has never failed to explode a corpse.
If you PL'd to 50 just to get an "epic" thinking you'd be �ber, you're going to be sorely disappointed with the HEATs, because the VEATs were designed so that anyone with one good finger and a braincell can rock the toggles.
I actually have one key bound to target the corpse, and another key bound to drop me off any form I'm on and execute the power... it works perfectly, or at least used to work perfectly before the recent increase in Lag which seems to worsen with every new Issue. 
But yeah... use two keybinds, it's more complex perhaps, but keeps your Warshade healthier in the long run. 
I believe that a Kheldian Gold Standard should be based on SO's, and for anything above that... there's Platinum!
Save Ms. Liberty (#5349) � Augmenting Peacebringers � The Umbra Illuminati
Save Ms. Liberty (#5349) � Augmenting Peacebringers � The Umbra Illuminati
So I made this bind:
bind numpadenter "target_custom_near defeated$$powexec_name "unchain essence""
And it doesn't work. In fact, it landed me in a hospital twice now. For some reason no matter how much I mash the enter key, the nearby corpse is only intermittently targeted and/or the power doesn't go off.
What's the problem?