I love that little "Stealth" from Tesla... I only wish it were VV/VW. If it were, I'd probably have four or five of them by now
I found it does best with a 0.8-1.2 Ohm coil, with 1.0 Ohm being the sweet spot (for me). I have mine with a Russian 91% at 1.0-1.1 Ohms, and it is working very well... but you are correct that it falls off quickly in the latter half of its charge...
I can live with the fall-off, though, because it makes up for that short-coming with it's size and I love the VTR-ish "protected" tank style... it fits great in my jacket pocket, back packet, or tank-bib-bag on my motorcycle. The submerged/protected tank is the only reason I ever wanted a VTR, well, that and the fact they are great self-defense weapons, lmbo