Not exactly sure what you mean by really thick shatter. If it's shatter, it's not liquid, so the viscosity doesn't come into play. If you mean thick shatter as in thickness dimension wise, that doesn't matter. Just break off a piece for the size dab you want (smaller then you'd normally use on a torch/nail setup).
It seems most people prefer low temp dabs with the EVO. I'd suggest starting at noon, and then experimenting from there. It definitely helps to have a heat-soaked EVO (on for 15+ minutes, so there's plenty of thermal mass). Drop the VXNail in, wait 8-10 seconds, and then inhale. Some people like to shut the EVO off when the light goes red, to prevent scorching anything.
I've found, that if you want to take a really massive hit, a little higher on the temp dial is helpful as well.
I believe if you search
@Enchantre 's posts in this thread, you can find where she gave some very helpful instructions.
Welcome to FC!