Yeah according to that chart, it looks like I'm maxing out the pipe right now. Maybe I'm just expecting too much of this pipe throughout the low and mid range after reading all the reviews, which is why I keep tinkering with the bike trying to get it to hit the Powerband harder. For all I know my bike is running as best as it can with my setup and I'm just expecting too much.
I did come across this thread: https://www.mopedarmy.com/forums/read.php?7,3730800#msg-3730835
It looks like this user had a similar issue, trying to find out what was "normal" for the proma pipe as he was lacking top speed. I noticed he said that they adjusted the clip setting on the carb, and at one point it was too rich on the top end. I'm going to adjust my needle clip to the richest setting (bottom of the 4) and give that a whirl since I can't seem to get it 4 stroking. If nothing changes or it's worse, I'll have to wait and see how it runs with that 17 tooth.