When not being close or looking away from it its always 0.00 (maybe 0.01 if you have alot of them),
When testing 1 visible at the same time it was 0.03/0.04, with 2 visible on the screen at the same time it was 0.05, I have never tested 5 visible at the same time and I dont think anyone will need it.
EDIT I now tested it with 5 of them at the same time (I dont think anyone will ever need so many though) But I got 0.07 whilst drawing all of them:
0.00 when far away, will be trying to optimize the resmon when far away though since it seems to jump up to 0.01 sometimes.
I have now also tested the resmon with having 100 of them running in the background, which also sits at a steady 0.01 / 0.00 
0.10 whilst running 1000 individual prompts in the background