And certainly from my experience they seem to process upgrades based on the paid rate.

On sub-A$200 rates I think I've only ever received an Exec or Deluxe/Deluxe Plus (certainly if booked as a Guestroom not GuestroomPlus)

Slightly higher I've sometime received the Relaxation Room (which is a double room and listed by the hotel as a suite which I think is fair enough - https://www3.hilton.com/en/hotels/new-south-wales/hilton-sydney-SYDHITW/accommodations/suites.html)