I am using MG with MC in my Earthboxes, and the trick is to moisten it as you are loading it into the container. When it is dry, it won't "wick" - - it needs to be moist in order to do its thing.

You could also saturate from top watering, and in a few days it will penetrate throughout the container - - but that is a brute-force approach.

In my containers, I actually found MG with MC too "hot" in terms of wicking action (moisture meter was always reading "Wet"), so I wound up doing a 50/50% mix with Sta-Green Potting Mix (without) Moisture Control, and now my moisture meter reads in the mid-range "Moist".

Raybo

Both peat and pine bark become hydrophobic (water repellent) when the moisture content of individual particles drops much below 30%. When this occurs, it's difficult to rewet. The best approach is to dump the dry soil into a wheel barrow or tub, add what you think is enough water to dampen the mix, mix the water in, and allow it to set overnight while, through diffusion, the water moistens the soil evenly.

The mushroom compost may not have been the best idea. It breaks down quickly and is usually very high in soluble salts from the heavy urea feeding it received before it made its way into your pots. Additionally, when the moisture control feature of the soil kicks in, the addition of the compost may turn an already heavy soil into a very heavy soil. You may find it helpful to wick your containers until roots have fully explored/colonized the lower parts of the container & the length of time a perched water table affects the root system is diminished.

Al