when a player is determining a piece of the setting is he roleplaying in that moment? He surely is advocating for his character - but is that roleplaying?
It depends what the process looks like. Upthread I've discussed a variety of ways that a setting element can be determined. They are not all the same.
If a player spends a chit or token so as to be permitted to point to a bit of map and say
That's where Evard's tower is, I don't think that is playing the character.
When I say
Don't I remember Evard's tower is around here? - thereby triggering a check on Great Masters-wise - that is playing my character.
When a player in the BW game I GM said
I look around - it's a mage's bedroom so there should be a vessel to catch the blood in that was playing his character (both stating his physical action and associated mental state).
Here's an example of 4e D&D play that I posted way back in
@innerdude's epic "dissociated mechanics" thread, and in some other 4e threads around that time, that caused a bit of a flurry:
The PCs were fighting some NPC hexers. One of the hexers used his Baleful Polymorph power on the PC paladin of the Raven Queen. This had duration "until end of the caster's next turn". For the next cycle of initiative, there were the inevitable jibes from the other players about not slipping on the slimy frog, etc. Then, at the appropriate point in the initiative cycle, I described the frog turning back into a paladin, just as the rules required me to.
The paladin's turn then came up, and the player, in character, made some rude remark to the NPC hexer. The hexer replied to the effect of "I'm not scared of you or your mistress - after all, I just turned you into a frog." The player, in character, replied "And my mistress turned me back" - the obvious implication being that his mistress, and him as her vessel, are more powerful than the hexer's petty magic.
That player's play - actually the same player as the one whose PC looked for the blood-catching vessel - was all done thinking in character. The player at all times was speaking as his character, thinking as his character, giving voice to his character's convictions of the Raven Queen's divine power. (It's also worth noting that the 4e mechanics did not contradict him: the mechanics leave it completely open why, within the fiction, the Baleful Polymorph ends when it does. In the example I've given, we see the player filling in that fictional space via in-character roleplay, thereby reinforcing rather than forfeiting immersion.)