RE: 17mm seems to lose top end speed
The LRP Spec III in the picture is my third that I just broke in. I just removed a screamer that had 7 gallons on it for my hot backup. I still have my very first LRP Spec III, also with 7 gallons.
I place the head so that air passes through it. If you have a LRP head handy, check it out, it will become apparent whey I have the head installed that way.