I must admit McLean is being shoehorned into the side at the moment because of his vigour and presence. He is a square peg in a round hole. Stewart is where he should be, it's just that he is out of form at the moment.
Tell you what look at this team. This, in my view is a team that matches the formation with everyon in their correct position:
Mannone
Rosenior Chester Hobbs Dudgeon
McKenna Evans
Brady Koren Stewart
Lambert.
Now I know we don't have Lambert but that not relevant to the point I am making. Lambert is a specialised lone striker. Fryatt is not. Brady and Stewart and fast skillful wide players who can both play on the right or left, Koren is the creator in the hole behind the striker. Don't confuse form with ability, I know Brady and Stewart are not playing well at the moment, this is about ability and use. That side would walk this league. Who is the player in that side we do not have? Answer : the lone striker and it is that that we need.
In answer to you last point, in the last 5-10 minutes of games when substitutions occur and games become strtched as players tire, formations become blurred player find more space. So, Yes, I think a seeming 442 formation providing more clear cut chances is a coincidence. I think they happen for different reasons.