Well, it depends. There are always exceptions to the rule.

The 20cc would make perfect sense on something like a Great Planes Stearman. There is plenty of room to mount it and the plane needs the nose weight. The 20cc would fly that airplane very well. It might even work good on certain warbirds with a nice round cowl. Iwouldn't try to put it on a .60 size trainer or your average .60 size sport plane though.

The 20cc might also work well on something like a very large trainer, large Decathalon or giant scale Cub too.