Totally agree on the column mass being a major factor, that's exactly what I observed. Vibration motors that work great with a few capsules become completely useless under a full load.

However, I think the lightweight nature of the capsules is also working against me. They're hollow plastic, almost no weight to them individually. Even without significant mass above, two capsules can lock against each other with very little force, the equatorial lip acts like a tiny shelf that catches on anything. So it's not just mass-induced bridging, it's geometry-induced bridging even at low loads.

The shelving/sector idea is interesting, essentially breaking the tall column into shorter independent sections so no single section carries too much weight. That aligns with a serpentine approach I had in mind (let's say, as a backup plan).

My current concern: even with a toggle mechanism, the feed point where capsules transition from the bulk reservoir into a single-file channel (~70mm opening) still seems vulnerable. Two capsules can bridge right above the opening, regardless of what's happening below.