Sidwell is convinced Propper will continue to improve as he settles into the Premier League, following his arrival from PSV.
He told The Argus: "When he first came it took him a few games to get up to speed with the Premier League, as it may have done with the majority of the squad.
"More so with him I think it was the profile, the money paid for him. There was more of a spotlight on him, but we can all see now what a good player he is.
"He is complementing Dale in there. The two of them work off each other really well and I think slowly, slowly, game by game, you are going to see more and more of him.
"He is still finding his feet but there is a lot more to come from him in all-round play as well as scoring goals, because we know he can do that, so it's encouraging.
"With the more games that go by and playing week in, week out, the more he is going to get comfortable, especially at home.
"I think we'll find he'll be playing vital parts in the majority of goals, whether that is starting them where he has won the ball back or with assists or even scoring himself."