Hey Nik.
I had tried it both ways.
I went to edit and then switched to RAW then opened the extensions and it selected the jpeg.
I then tried a different images switch outside of edit to raw, then went to edit and opened the extension and same thing, it selected the jpeg.
I have however found a bit of a work-round that is a bit less painful for the moment then doing them one at a time.
In photos,
Select all the images you want to switch. then switch to raw. All images switch to say Raw-Jpeg.
Then open up Raw Power and you will noticed that the arrow icon on the thumbnail is present next to RJ (I assume this means that file has been edited)
Anyway, just select all the images you just switched to Raw in photos, right mouse click and select revert to original). It will batch them all and once done that little arrow is now gone.
Go back to Photos and click on edit on one of these images, open the extension and it now selects the Raw file.
Not ideal but it works.