Losing the calibrated leak is really nitpicking and should have no noticeable effect on the idle. Just going a step further, when hooked up as you first suggested will also have minimal effect. It is not technically the same as having a vacuum leak at the balance tube. The vacuum leak you create at the balance tube is using air that is passing through the AFM. The net effect might be a slightly higher idle rpm. The effect would be similar to how the air regulator bypasses air into the balance tube that is coming through the AFM to increase idle rpm. Rpm might change but idle mixture should not change.
