[cecile]

I think replacing brass nocking points by coloured threads of polyester may be an improvement. It will minimize friction with the tab and reduce (a little) the weight of the string.
As for the spacing, I increased it on my tab mainly to prevent any contact with the nock of the arrow. Depending on the finger pressure, a finger may slide against the nock and disturb the flight of the arrow.
Anyway, if you wish to keep your brass nocking points and you don't touch the nock with the tab, managing clearance on your tab is a good idea in order to prevent friction. You may see no effect at short ranges, but it could have some at long ranges.