The inlet port and reed is very tricky to model correctly.
Look at the RZ400 inlet for my F3 bike.
The 39 dia is the actual area at the reed block face ( less the divider ), the 41.5 dia is the effective reed block flow area.
The 35mm is 2/3 of the reed block length, this models accurately the stuffer.
At the other end is the carb trumpet with a 6mm end correction length, this 6mm at 69mm dia is the flow area curtain at the carb entrance.
Using this setup you get the correct effective length of the inlet and the waves bouncing up and down the tuned lenfth are timed correctly.
In reality my "rubber boot" is bigger in diameter at the reed face, but using the effective diameter less the divider sets the actual area as seen by the flow.
This info was gained off an instrumented engine used for a PhD project at AK Uni, and initially I left the reed length off altogether, and added 1/2 the carbs trumpet dia at the other end.
This gives approx the same length overall.
But the method above is more accurate for all engine and reed sizes.
YOU'RE BEHIND ME COS I'VE GOT A WOBBLYPIPE - I had 50 of these T shirts to give to World and National Championship winners , sorry all gone.