i think you are getting too hung up on the photographic numbers within MR. it appears to me that in MR they basically feed into an formula which gives an 'exposure value'. for EV 8, as you mention, there are multiple combinations of iso, f/stop and ss which should, theoretically, produce the exact same exposure. its not an exact science though, and MR obviously haven't perfected the formula yet. MR seems to pick one of these combinations at random, and whilst varying between these potential combinations should produce 'approximately' identically exposed renders for the same EV, in practice it doesn't.
get a camera. they've had centuries to perfect those
