Yeah, I'd never use MGMC for a "self-watering" pots. There's too many things that can go wrong. The few instances in which I've used such pots, I use the supremely well-drained gritty mix. Water slowly/weakly wicks through the turface or diatomaceous earth in the mix, but without creating a perched water table. This allows me to use the gritty mix indoors without have to water every day.
Q