I endorse what Rutty has said but I think he meant visibly twice the perceived gap at the rear not actual measurements, that would be a massive gap. I run what are considered wide gaps on my pistols, with an average sightbase for example I'd have a 4.8 mm wide forsight with a 5 mm rear gap which gives the picture of the sight in thirds with the observed gap either side similar to the width of the observed forsight.
I'm not sure thats any clearer! But anyway go big foresights and big gaps most people prefer it although it is personal preference and you'll always find someone who uses tiny gaps.
Good shooting,
Robin
Walther KK500 Alutec expert special - Barnard .223 "wilde" in a Walther KK500 Alutec stock, mmm...tasty!! - Keppeler 6 mmBR with Walther grip and wood! I may be a Walther-phile?