In my experience the oil get aireated and that is what mostly contributes to the volume expansion in the oil tank. The more oil you have in the tank to begin with the less room you leave for this expansion to not overfill it. There is alway more than enough oil in the tank to supply the gravity-fed primary oil pump.
I do not see any reason to fill up to the top of the dipstick at warm idle unless the owner/driver is someone who likely will not care and check the oil level during the service interval. In that case you buy her/him a little bit of safety margin that the engine won't run dry due to oil consumption. Two additional quarts could mean another 3000 miles before trouble hits hard
at normal oil consumption levels.
Other than that I'am curious if someone has ever recorded an oil consumption/1000 mile vs. fill level chart. I bet at some point closer to the Full mark consumption/1000 miles goes up quite a bit.
Ingo