That's the opposite of how I read it:
Section 84 allows the settlement committee to grant authorization to Immigration officers to issue fines and close the matter without taking it to court.
But regardless of this my point is; the Immigration act is the legal framework setting out duties and punishments surrounding immigration matters. Immigration have been granted authorization (via police orders) to issue fines for transgressions against the act, but they cannot be granted authorization to issue fines in excess of what is legally set out in the Immigration act. When the act states a maximum fine for a transgression, no one can fine you more than what is stated.
Also from the Immigration act:
This is why, when years ago Immigration increased the daily fine for overstay from THB 200 to THB 500, the maximum fine was left unchanged at THB 20,000. To increase the maximum fine for overstay would have required amendment of the Immigration act, which is a lot harder than just issuing a new police order.