what's at play is the minor radius. The smaller, the further it can get into the modulation (left /right). Having said that, there isn't a piece of vinyl that a stone with a minor radius of .3mil cannot read.
The original minor radius of the Shibata was .3mil, would read the 40K or what ever carrier signal was cut into quad. A more critical parameter is the relief cut in the stone at the leading and trailing sides.
Which is what was accomplished with the Shibata. meaning there was less chance of the leading side of the stone to come into contact with the modulation before the scanning area did. That was furthered with the fine-line/micro-line etal, as relief on the trailing side was greater than the shibata, furthered still with the micro ridge design. Due to the amount of vertical scanning area of the minor radius, the minor radius could be made smaller, yet create bigger contact patch which reduces wear on the stone, and vinyl due to less pressure on both.