IMHO,the whereabouts of a holding call by R on a punt would/should fall into the "when in doubt" family and ruled to be downfield unless absolutely sure that it occurred behind the LOS. I've botched two PSK enforcements since it came to town (2003) and this was half of 'em :
(1) 4th & 5 @50, K punts ; flag around 50 for holding on R; K rolled dead @R's 20; moved ball to R's 10 and gave it to them; a few plays later I began to ponder, "did the foul occur on/behind the LOS

;I later felt bad about my mistake until I realized that the coach made a mistake ,too - He thought I knew what I was talking about

. K won the game.
(2) 4th & 10 @50, K punts; R waves both hands & is

for invalid FC signal @ R's 30; punt lands untouched @ R's 32 and rolls dead @ R's 35; we mistakenly enforced the penalty from the end of kick -R's 35 while it should have been from R's 30 under ABO; I discovered this in post-game; I didn't feel as bad as I did on botch #1...

. K also won the game.
Morale of story : Remind the

to remember where the foul occurred -even if they don't need to.
Remind yourself to ask where the foul occurred, especially if you need to.