Pete, (you can never have too many Pete's : )
I use purchased fertilizer (Miracle Grow and Esopma) mainly on potted plants and Espoma only in spring on in ground plants to boost the beneficial bacteria and fungi (mycorrhizae). Miracle Grow is used mainly to push growth in seedlings and young plants. The rest of the year its "cut and drop", cover crops or compost. I've top dressed with rabbit manure, with good results. I never use slow release fertilizer, because it has to be mixed into the soil to be completely effective (break down), and that would damage the surface feeder roots.
From my limited experience with figs, the method for fertilization that I will be using in the future (on established plants) will be to top dress with 2-3 inches of compost. It will be renewed regularly when necessary. From observations a lot of feeder roots develop at the surface of my 5 gallon buckets, just below the surface "bark mulch", they multiply within the top dressing of Espoma, Limestone and potting mix.
BTW the Espoma or any balanced fertilizer and micronutrients with Dolemite Limestone would work fine on established trees without any additional amendments.