What if you were to mill the basic shape(s) out of foam and put them to the test? Mount them in the intake of your SR, put some streamers on the end of the cone, set a high speed fan at the intake and let it rip. Then observe the streamers from the exhaust end and see which setup is less prone to turbulance i.e. which streamers are more smooth in the airstream. Cant be any worse than the speculation so far

mb