Kev, I have several mature figs, and I agree that the miracle gro will dry out quickly. In east Tx (you are not too far from where I am in the Big Thicket) figs really don't need amended soil. The soil in your video looks typical of east Tx, sandy loam probably with deep clay. I hate to suggest it, but you might consider taking the trees up and simply planting them in the native soil, without amendments. The native soil will stay moist longer and doesn't have peat in it, which once it dries out is hard to re-wet.
Figs really aren't massive feeders either, they're not like peach, pear, plum or other fruits that require regular fertilization. Figs originated in Western Asia and the edible fig Ficus carica especially in the middle east and mediterrenean where soils are sandy and somewhat poor.
I basically never feed mine except when I feed the lawn a couple times a year with a hose end sprayer, I'll spray around the trees. Some experts recommend raking leaves up under the trees in the fall and letting them settle and turn to compost for nutrition. I do that with oak leaves. In the wild, that's pretty much what happens with their leaves anyway.
One last suggestion---1/2 gal. water at planting time isn't enough. The surrounding soil will absorb most of that water. When you plant, you should fill the hole with water first, let it all soak in, and then put in your tree and back fill with soil and then water again. And in hot or windy weather (the breezy, windy, low humidity weather we've been having the last few weeks has been horrible in drying things out) you may need to water every day.
Just my suggestions. I've been growing figs for many years and had what was at the time one of the largest collection of edible fig varieties in the state. I had 67 separate and distinct varieties growing and all but about six were mature and fruiting. Unfortunately, the drought of 2010-2013 coincided with me being in an accident that caused severe injuries and I was not able to take care of the orchard and lost quite a few.
Of all of them, I never planted any in amended soil unless it was in order to make the soil more porous by adding sharp sand for a few varieties that were native to Afghanistan, Iraq and that general area and which needed immediate drainage the way olive trees do.
Anyway, just my suggestions.