The minimum edge width of 1m is set to to allow further blending ( if necessary) and to counteract the way GE paints a 2m terrain section, however if you wish to set a lower value then adjust the following line in the Terrain Paint R script
Line 108 --- if edgeWidth >= 1 and i > offset then
to
Line 108 --- if edgeWidth >= 0 and i > offset then
However because of the way GE paints the terrain the edges will not be smooth or as easily adjustable compared with the 1m distance.
For example set the Terrain Editing Brush to 0.25 (equivalent to a 0.5m distance) and try painting a curve and you will see that it misses sections.