The narrower gap results in more "points closed" time and gives better coil saturation for a hotter spark, supposedly. .020" is a good midrange setting and it's easy to remember. Try to use a round wire gauge, rather than a flat blade if possible. Any roughness on the surface of the points will result in getting a wider gap than the gauge indicates, and a round wire gauge like the old style pocket spark plug gappers also worked well for points.

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Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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