I'll force myself to say only this: if you want to spend this much time obsessively repeating a single technique, it had better be something that actually produces real music, rather than the "rules of counterpoint" from Gradus ad Parnassum, which no "master" has ever abided by.
If it's Dorian, which it looks like, how could it start on a G and a D? If you follow through the rest of the cantus, it doesn't make sense to start on a "G chord". Examples like that pretty much always start and end in the same 'key'.