My TSR25 came with the riser so I have no idea what one would need to be added.
but I do use the flip up sites too. That way there is no issue with fitting a cheek pad for one shooter. 3 point sighting.
The primary arms (not micro dot) I purchased years ago came with a riser as well. He came and asked me, so I told him I would ask the folks here for him.
My PA micro needed a riser. I have it co-witnessed with the front F post, and it's spot on.
After measuring twice and cutting once, this is the one I got-
[h=2]Lion Gears Tactical Slim Low Profile 0.75" Riser BM0607EX[/h]
I don't go for quick detach, and I didn't want one that covered the top of the entire upper. Just big enough to hold the sight.
I'm real happy with it. Well built and stays put.
The .75" is the key measurement whatever you get. Most flip-ups are made to co-witness with an F post, so something along these lines should work.