While using a poly aftertouch keyboard, I noticed that whereas the channel AT produces a smooth variation (on a filter, in my trial), the poly AT produces a rough one, as if some smoothing of the MIDI AT messages was in action in the first case but not in the second.
Also, the poly AT seems to have more impact than the channel AT.
To check this, just assemble an origin oscillator with a half closed LP filter.
Could the channel AT have benefited from a preferential treatment?