Andy , with the usual caveat that it's unfair to judge negatively on the basis of a pic . I reckon they look natural . Pics 5&6 here are similar .
http://www.themodernantiquarian.com/site/14271/non_rock_art.html
It looks like a sharp edge with the sides steeper rather the more usual inverted cone shape more typical of cup marks . Although not obviously on a bedding plane , unlike those above , they are on the same "line" and adjacent . They and those above may well be the reason for choosing the that particular rock .Pity about the missing rock ,were they similar ? and they did have other possible (later ) markings .