The Rotax Airbox did not fit to my installation at the beginning. The airbox conflicted with the motor mount.
I long considered how to solve the problem. Discussions with motor specialists and the distributor followed. Some did not suggest a change to the original design.
I solved the conflict by using 30 degree elbows of silicone hose, available in car tuning shops. I am pretty sure the installation does not decrease the engine power. At least I now have a good understanding how the airbox works and how it helps to improve engine power (stationary wave which leads to a light turbo-charging effect). So my modification will slightly change the wave frequency. The optimum charging effect will thus be in a slightly different density altitude.