TH Procing

[Dihlyte]

Furthermore:

Applying TH 8 then removing your TH gear, will lower your chances to proc to 9.

Applying TH 8 while using TH 8 total will reduce your chances to proc to 9.

Applying TH 8 while using TH 9+ total will maximize your chances to proc to 9. (Anything less will lower your chance, anything more will not increase your chance.)

Procing to TH9 then using TH9 total will reduce your chances to proc to 10.

Procing to TH9 while using TH10+ total will maximize your chances to proc to 10.

So on so forth.

This is clearly stated by the developer.

So if we are to make a random assumption, it can be determined:

TH8 when using TH8/9 total is 100 chance to be applied.
Procing from TH8 to TH 9 while using TH9 equipment grants access to the maximum "set rate" value of let's say 25%.
Procing from TH8 to TH9 while using TH8 or lower total reduces your chances to proc to TH9 from 25% to any value less than 25%, such as 20% in TH8, 18% in TH7 etc.

Or simply:

TH8 (Mob) TH9 (player) 25% chance. (The maximum set rate)
TH8 (Mob) TH8 (Player) 20% chance. (An example of the reduced rate)
TH8 (Mob) TH17 (Player 25% chance. (An example of utilizing additional equipment)

(The above values are simply for representation purposes, and do not reflect actual values in-game.)