Well, of course, you got the idea. What winning chance would you like to have against 20% weaker team with no manager attending? I would say 70-80% is reasonable. But I usually manage to win something like 19 out of 20 matches were my team is 20% stronger and I'm attending.
Of course not, I feel that I can change the course of the match. But because you changed your winning chances from let's say 70% to 85% - that still does not guarantee you a win. Lets say you are down 1 goal, and you made some correct decisions and now you dominate the match - you still might get an upset, because when player is 1-on-1 with goalkeeper "roll of dice" is happening - and you still might get unlucky and roll 1 three times in a row