Mulch donut question

How much space should there be between the tree/shrub and the inner mulch ring?

I’ve seen recommendations to leave a few inches of space, or it might cause rot. But, I’m reupping wood chips on a large number of trees and I’m already seeing a lot of grass/weed growth next to the trunks/stems of the plants where I left this space. Also I’ve read that bare soil is bad, although I’m sure this mostly means on a larger scale.

Seems like I’m choosing between rot, weeds or bare soil right around the plant trunks.

Thanks!