The link below uses an XR1200 to demonstrate that shorter air inlets increases peak power and longer inlet increases peak torque and shifts it toward lower RPMs.
XR1200 Intake - The Effect of Different Length Velocity Stacks
I thought split FCRs are popular among our race-spec bikes because of the overall shortened inlet tract + blue velocity stacks (short) which increases peak power, and racked FCRs maintain the long, OEM runner length thus providing more torque which is useful for road riding.
there's another page to that with some photos of the setup, which makes it more interesting (if i'm reading it right). good find samadhi.
XR1200 Intake and Velocity Tubes
here you can see that the bend he is talking about that makes a difference compared to the modified airbox is the white plastic 90 degree bend that is stuck onto the throttle body inlet. without anything on the throttle body (shortest) it makes less hp that with the modified airbox, probably 2hp on average across the range. with that bend fitted only (no airbox), it makes 5hp more peak and 3 - 5 through the range compared to the modified airbox, or 5 to 7 more than with no bend, just an open throttle body. so adding the first piece (an extra 4" of inlet length) helps it a lot all over. which is probably a similar shape and length to the rubber tube that goes between the oem hm1100 throttle body and airbox, and which soko has his corse dynamics stacks fitted into.
and then, from there out, it follows the generalisation that more length moves the power down the range. in reality, tube 4 would be the go for most people. it'd be significantly stronger in the midrange, and makes the same power as before at lower rpm, so good for the motor. and i think if he'd used tapering tubes as he went longer he'd have found less hp loss while keeping the torque gain.
surprising that he found that the radius on the entry made no difference. i would expect a good entry to make a difference, but it was possibly a case of access to and room to fit. putting a corse dynamics stack which soko has in there would make a difference i would expect, but in reality there's no room to fit it and the filter.
i think the first bit on a throttle body or carb is always handy. i added 100mm ram tubes to the phm40 carbs on a guzzi sport 1100 and it moved the torque peak down a touch, but didn't hurt hp or the rpm it was made at.