Some rails have a slight relief (1/32"?) between the feather strip groove and cushion so the cloth is flush with the top of the rail. Others don't have the relief and the cloth is slightly proud of the top of the cushion. Rails without the relief are probably easier (cheaper) to make, is that the only reason you see them (though I also don't like rubbing my shaft against rail wood on some shots)? Any advantage of one design over the other?