In my experience, dosing anywhere around the retention ring line in the basket has the potention to cause channeling. That is, right at the ring, slightly below or slight above. We had this problem for some time & no matter which barista was on shots, channeling could occur at any time. We have now eliminated this situation entirely at the cafe by replacing the stock LM double baskets with Synesso doubles that do not have a retention ring indent. So now, dosing up or dosing down, channeling is not an issue. Also the added benefit of using the Synesso baskets is, they knock out very cleanly & with much less effort, thus reducing the noise level. They also work very well in the LM Swift grinder whereas the LM doubles work, but not that well.
Beginner and pro baristas share tips and tricks.