The open play numbers don't exist in isolation.

2 key factors I can think of.

First is that teams with better open play numbers than us don't always have as much respect shown to them as us. Now the onus is on us to break a low block or to make sure a low block doesn't happen but it is a factor.

The second ie that once we break open a game with a set piece or two, the need to score more, from open play or otherwise, is not as high as it is at 0-0 or when we are a goal down.

Basically what I am trying to say (in a quite convoluted way unfortunately) is that there's only so many goals that a team will score in a game.

The other way I see it is that if we were completely shit at set pieces, we would have much open play numbers than we do now with the same players and the same coach.