Regulation 1178/2011 on appendix 8, helicopters say that if you are making a renewal or revalidating a MPH IR, that IR is valid for a SE and SP/ME rating that you have, if in the previous 12 months you did 3 flight with IFR approaches on a SP helicopter.
What is written aswell is that to convert the IR from a SE to a ME you need the 5 hours that you are talking about. The other way around you don't aswell as from MP to SP. In the appendix 8, previous mentioned you have credits from a MP to a SE and to SP/ME.
My understanding is that, once your ME/IR is valid you just need to make the type rating of the A109/SP-3hours ( MET to MET), the two hours in IR and the profcheck.
Best regards,