civil radar controllers where they will make clear you're on a FIS but will give you very accurate traffic info based on radar
If you want accurate traffic information based on radar you should ask for a RIS. The very reason RAF controlers don't tell you are identified is because a FIS is (and I quote) 'a non-radar service provided, either separately or in conjunction with other services' and further down the page ' The controller may attempt to identify the flight for monitoring and co-ordination purposes only. Such identification does not imply that a radar service is being provided or that the controller will continuously monitor the flight. Pilots must be left in no doubt that they are not receiving a radar service.'
"to maintain prescribed separation between aircraft participating in the advisory service"
The controller also needs to avoid traffic that is not participating in the advisory service unless co-ordination has been obtained. With co-ordination/agreement of pilot separation can be reduced to 1000ft and in some cases 500ft for military controllers.
he descended the IFR to but 5000 would have been acceptable for his descent profile at that point
Did you see the IFR traffic and are you current on the type? If not can you be sure what was acceptable to another pilot?
Regards
Pie