I am sure that is the case if the air is being blown in by a blower or turbo. If the air is being sucked in by the down stroke of the piston, I thought it would "pull" the air and actually make a lower pressure and less air density.
i dont think vacuum would change in the cylinder only on the port itself, and since the intake is being epoxied smaller in diameter the vacuum would be greater on a smaller port....this is where a good porting would come into play. not only porting the intake tract smaller but also increasing the venturi effect inside the port versus the measured vacuum from the cylinder.
but....im not an engine builder. just want to keep throwing that out there until someone with porting experience can chime in.
Without reading the entire post. Hcomras is on the right track. I think it has been stated that the rotax flows too much air. That is why the epoxy is needed. To help with the velocity and more of air to fuel ratio.(ie. too much air less efficient fuel burn). I think density has more to do with temp of the air comming in.
But like Hcomras I'm not an engine builder either.