Playing 2/1 , the response of 1NT to 1M open should be defined as F1 or NF.
Obviously playing that 1NT response is unlimited it must be F1.
Let's focus on playing that 1NT response is limited. While 1NT response is limited it's upper limit is usually 11 HCP some play it also as bad 12 HCP. Please ignore this nuance in your responses.
Playing that 1NT is limited – it can be played as F1 or NF. Each attitude has its advantages and disadvantages. May be one way is superior playing IMP and the other is superior while playing MP. Is it just a matter of style and in practice the overall results of both are close? Can you quantify somehow by how much one way is better than the other? Please state your opinion on the subject and make a vote. Vote according to what you think is better, regardless of how you play it.
Plus... it's free!