I hadn’t thought of temperature effects, but that’s certainly possible.

My theory is that by having similar sizes particles, there is less micro-channeling. I think there is this weird bit of espresso extraction that’s like a jet engine, the weight is changing during the shot as coffee is extracted. I suspect there is some interaction with channeling as a result.

I think this is why staccato tamping is better than a normal shot because it uses pressure to help. Ultimately, this layering modifies the internal pressure.