We're using soulshards for 1.8.9, with the plan of including it in a pack.
When playing with the altered configs for soul shards we discovered that the textures for soul shards do not extend to the full possible range.

You must ship your own blockstate json and textures.

would I put the custom blockstate.json file in the ./config/sstow folder?

A resource pack

I've had little success with this. I tried copy/pasting the tier 5 entry in the json, editing the "5" to "6" or higher, but I still see no textures, even with a resource pack.