I'll second the idea of experimenting. People get such different results that you can never tell about your own books without trying.
With regard to fantasy readers only being interested in doorstops, that's more true of epic fantasy readers. Shorter works of urban fantasy don't seem to have that problem. I've read some that are selling well that to me feel very short.
Even if one isn't doing especially well wide, there are some arguments for leaving at least some books wide. The principle one is trying to build a little presence outside Amazon in case something catastrophic happens. I make very few sales in wide, except when I'm promoting heavily, but I keep one series there, as well as my nonfiction titles and a couple of shorts (which don't do well in KU anyway).