Tank heater tested and as I had feared, the heater had been installed too high in the engine compartment by my helper and well, I guess you can only expect what you inspect. I thought I'd test it and see if it worked in that weird position. No circulation.
So today I worked outside in a balmy -10C and set it as right as I could. Tank heater relocated to front of car, passenger side right behind my radiator fan shroud and level with the bottom of radiator. Sorry, there just isn't a good spot for one of these in a Civic. There's a few inches of clearance from the engine. I hope it's enough. I zip tied the heck out of it to the shroud and an insulated line from the a/c unit. Nice gradual slope all the way up to the heater core.
I'll test it in an hour or so as the engine has to cool from the coolant refill and air purge.