Hi Rik,
I applied as a secondary applicant on my partner's 186 visa. We didn't submit any documents confirming my dependency on my partner. I have a full-time job and fully supporting myself. We don't even have a joint bank account.
I provided a few documents proving our de facto relationship: photos, joint lease agreement, transfers between bank account to each other (eg, I'm paying for all of the bills, so I just sent our MA screenshots from my bank account showing that my partner did transfers), itineraries for travelling, etc.
Hope this helps.