In my understanding a "Petroglyph" needs to remain (or have been intended to remain) in situ on "living rock" or be inscribed on a free standing "boulder" which largely remains such in form. Once significant "shaping" of the rock on which the inscription has been made takes place or the incision takes on a 3 dimensional aspect it becomes something else - e.g A Bas Relief or a Stelum. Also it should be an "image" rather than "script" which a Rune is.
Clearly the derivation of the word could include any and everything carved on/into "rock" - but does adopting such a definition really add any value? (Michelangelo's Statue of David as a Petroglyph - well it is carved into rock!) Among more specific definitions found on the Web are
"A carving or line drawing on rock (especially one made by prehistoric people) "
" Petroglyphs are images created by removing part of a rock surface by incising, pecking, carving, and abrading."
" a drawing scratched or otherwise etched into a rock".
Significant "ideas" encompassed by these definitions are
a. relatively "light" carving - "incision", "pecking", "Abrading"
b. "line" rather than 3D
Such definitons are always imprecise. In other areas we have generally taken the view that we go for the most specific appropriate "Connection" and try to avoid duplicating connections using only slightly different terminology. Given the above nuances of definition and the fact that we already have similar assignments for the Madera Rider and Tiya is there any benefit in duplicating them? If there were clearly a more appropriate assignment then we should remove a site from the less suitable one but is that the case with any of these?