Got to disagree that age is the main thing here. I've seen monsteras throw fenestrations at a year old when they get strong light, and I've seen 6 year old plants with zero splits stuck in a dark corner. My guess is the move to that east facing spot plus the chunkier mix did most of the work, since light drives the energy for bigger leaves and the bark mix keeps roots from sitting wet. As for your friend in Seattle, tall does not mean happy, a stretched out plant reaching for a dim window can look huge and still never split. Give it a couple more leaves and you'll probably see the splits get bigger each time.

Does icing the mix actually help enough to matter, or is the 5am start doing most of the work?

Hear rich black traps poorly under 14pt on offset?