Having just spent a while doing kings for BB items, I'm fairly sure that the chance of getting a TH proc is higher, the higher your own TH equipped is.

If I start with TH7 and then swap gear to normal melee gear TH3 or 4 depending if I swap knife or not, the chances are that the fight ended up with TH8 or 9. If I full-time TH7, it seemed to rise faster and higher chance that it ended up on 11 or 12.

I've also taken to full-timing TH gear in dynamis until I get proc too. Apart from anything else (and it might just be placebo anyway) it reduces the chance of killing the mob before it's procced.