Ian, would you put any expectations on Blue 5's running line? Does it need to be straight (as per the blue arrow) or can he meander in with a pause or 2 on the way?
Answering for Ian, though I bet he can answer for himself anyway...
If he joins the ruck he must do from behind the hindmost foot.
If he oversteps that offside line and does not join the ruck but has a pause and then joins he has not joined from behind.
I know that the Jesuitically inclined can make a specious arguement to allow it - but I would have no truck with such nonsense.
Yep, no messing about!
If he oversteps the line, I expect him to have done so for the purpose of joining, then I expect him to go straight in and join alongside the HM player.
If he overstep the line, and then stops, I expect him to go back behind the line (he has about 5 milliseconds to decide) and then take another run at it.
If he is trying to make up his mind whether or not to join, he must do so while still on-side.
From the point of view of getting a better game, I would not want to discourage onside players who are a few metres either side of the ruck from joining it, by being jobsworth about the precise angle they join at, so long as they comply with 16.5 (c) and (d).
The more players there are in the ruck, the less clutter there is in the back-lines