No intrusion. Its sort of hard to explain, but I know it when i see it. When I say sits in space well and has an atmosphere it is all about value really, or correct value throughout the painting. The space looks authentic. Nothing appears to be floating or appear like flat cutouts.
Many times people will paint from a photo and copy the photo exactly without understanding that a photo is flat. Without a lot of life drawing experience photographic copies tend to lack what I am talking about above. If you do have a lot of life drawing experience you intuitively know when to deviate from it.
This explanation probably confused you more, but it is sort of hard to explain.