Question: 

When Robar has a Stun equipment set, which stun is calculated AND initiated(or not) first? The A1 or the set effect?

Qualifier: 

Ive read the guide posted by mod-Marius which details the many facets of Artifacts and how we interact with them. In fact, within that guide, it directly references the above question regarding an ability (like Robar's) which has a 50% stun chance combined with an 18%{?} stun-set proc. 

Im aware the chances are not combined, and the guide's verbage goes something like: "the ability's stun is calculated independently, and the gear's stun is calculated independently." This doesn't explicitly state which is first, lacking conviction in the order of those statements as having importance.

Why should you care(?):

Robar's A1-stun allows for an additional turn, but NOT if the stun originated from the gear's set-bonus proc, even if it happened as a result of his A1's attack. I know this because my Robar will occasionally stun with his A1 but not get another turn. 

If the set-proc is calculated before his A1's 50% stun, then that's quite a bit shit.. In that case the Stun set is more of a liability than an asset, as it interferes with the chance for him to get an extra turn resulting from the A1's potential proc.

Ideally it goes:

> A1 active roll 50% >

  >If yes> stun + extra turn + "yay!" ^^^

  >If no> gear roll 18% >

      >If yes> stun + "good dog" *END

      >If no> "better luck next time" *END

Hopefully not:

> Gear roll 18% >

  >If yes> stun + "wait, what-!?" *END

  >If no> A1 roll 50% >

       >If yes> stun + extra turn ^^^

       >If no> "haha loser" *END