Ok, if the dip tube is the problem then here is what you need to make sure of. The groove (imho) is not a deal killer. I would venture to say that you did not mount the coller from the Blichmann dip tube on to the hopstopper. This is more important than the groove. If you didn't, you must install that coller. It is the round clamp that is pinched tighten with the allen screw. This does 3things when properly installed.
1) it provides a depth setting so the when pushed in all the way, the groove will align with the o-ring.
2) because it has a dowel on the top (roll pin) it positions the dip tube straigh up and down.
3) and this may be the main reason for your troubles. It will keep the dip tube perfectly centered in the port so it does NOT wiggle, hang, etc. Keep in mind the Boilermaker does not provide a compression fitting here. This is why that coller is so important.
Now, my guess is that your dip tube on the hopstopper was NOT made at the correct height. If it were perfect, then the dip tube should be perfectly centered in the port as the other end it rests on the bottom of the pot. And I would venture to say that once you install that coller,than the hopstopper will not rest on the bottome like it actually should (mine does). Therefore the weight of the hopstopper may tug down on it. I would suspect a forgiving tolerence though.
Btw, the hopstopper resting on the bottom of the pot will not cause any kind of plugging. If you carefully at the end of the dip tube (inside the screen) you will see a notch cut out at the end of it.
Let me know if this helps.