fading parameters controlled by MIDI

i’m controlling the alpha of rectangles instanced over a grid with incoming MIDI on/off. i would like to have a controllable envelope, so instead of sudden on/off, i can have the alpha fade in and out.

i’ve done this before. my hard drive crashed, so i can’t look back, but i swear i did it with a trigger chop. it’s hard to explain all the ways this is going wrong, whether i put the trigger before or after my shuffle CHOP (set to sequence all channels), whether time slicing is on or off, but it is giving me a literal headache. i mean, i can see the trigger CHOP doing what it’s supposed to in the shuffle CHOP, but i don’t see this translate to the alpha.

any help appreciated.