I went to Russia in 1993 to collect the first ever Yak-55 export. While there I flew with Sergei Tatevosov in a Yak-52. We did several repeats of a power-on upright flat spin from a stall turn (right rudder) entry. The rotation, with right foot, left aileron and about half forward elevator is very frisbee-like.
The recovery taught me, and which I have since used successfully on Yak-55, and all 3 types of Sukhoi is to maintain power, change feet, then move the stick back, right and then forward. The stop is very sharp and takes about half a turn.
This has been repeated several times in the UK in different Yak-52s, with identical results.
The mirror image technique works on American-engined aircraft. I have considerable experience of this flat spin recovery at display heights in Pitts types, CAP-232 and -222. In all these instances, in-spin aileron is quoted in the POH for flat spin recovery. It all just works much better with power on.