You know if it is too close as it will get clouted by the lugs!!
The lugs corrode though so may not be the same height, so if you set it on a low one then a high one comes along and bang, or set on a high one then it is too far away for a low one.
Fortunately the tolerance is very good on the CPS on the cossie at 0.6mm to 1.0mm, which is 0.4mm leaway or 16thou in old money.
tabetha