You will find the location of the bypass hole is important
For instance, if you have a 90deg bend in the pipe between AFM and turbo then putting the hole on the corner such that the hole looks directly at the turbo inlet then it might help lean AFR out under load. At speed, air likes to travel as directly as possible.
Otherwise you want to look at using a re-scaling device like the jaycar:
http://www.jaycar.com.au/productView...UBCATID=965#11
It sits inline with the AFM 0-5v signal and gives you control over fueling at all load points. You still need the bypass else the AFM just maxes out. For a neater installation you could run the jaycar with a bigger AFM, one rated at 250hp say.