The answers provided so far - flying at 2500 puts you over, and not in, a piece of PRD airspace that is active SFC-2500 - are correct, but the supporting AIP reference isn't all you need.
By default, Restricted airspace is considered Class C below FL285 and Class A above that, "unless specified otherwise". In practice, unless it is associated with a military ATS unit, no control service is provided within most active restricted areas.
The answer you need is in MATS:
Originally Posted by MATS 2-30-1150
Delineate adjacent airspace as follows:
a. When one of the airspaces is controlled airspace, add the buffer to the navigation tolerances of air routes and contain within CTA.
b. When one of the airspaces is uncontrolled airspace, contain the buffer in the restricted area.
Originally Posted by MATS 2-30-1170
Aircraft operating at the vertical limits of prohibited areas and Restricted Areas/Airspaces are separated from activities within those airspaces.
There's also 2-30-590, which after a lengthy spiel about calculating buffer heights, concludes:
The promulgated vertical limits of Prohibited and Restricted Areas and Restricted Airspaces shown in AIP, FLIP and NOTAM contain these buffers.
Note that this is different to Danger Areas, where flying "on the limit" puts you in the Danger zone:
Originally Posted by MATS 2-30-620
The vertical limits of Danger Areas are the upper and lower limits of the activities within the airspace.
A similar distinction applies to the
lateral limits of PRD areas:
Originally Posted by MATS 2-30-470
The lateral limits of:
a. Prohibited and Restricted Areas/Airspaces encompass the activities of the administering authority.
b. Danger Areas are the extent to which activities may take place within the area.