Pingouin, who said anything about a Position Report? You Sir, are putting words in my mouth...
Ref AIP ENR:
11.1.3 Pilots of IFR flights leaving classes A, C, D or E airspace should,
before entering Class G airspace, contact the ATS unit providing
services in that airspace.
So, it should go like this.
"CEN, ABC, request descent" - because you are identified and in controlled airspace.
"ABC, cleared to leave control area on descent, no reported IFR traffic, passing 8500 contact CEN on xxx.x"
You reply.
Passing 8500 you contact the new freq. They don't need your estimate as you are identified so TAATS tells ATC the ETA. If they lose radar contact and can't work it out, they will ask for it.
I just don't get where you guys are getting your info from - "identified" = no position reports, "Radar service terminated" = position reports required.