What I mean is to allow NBT data to determine (or modify) the inventory size with rows and columns like in the config.

My goal was to have an extra column backpack only from dungeon loot, but coming to think of it it would also make the mod more versatile for progression-based modpacks.

From the readme:

For Modpack / Map Creators

Custom backpack size can be set using NBT tag backpack:{size:[x,y]}.
Custom armor value can be set using NBT tag backpack:{armor:x}.
Default backpack loot table wearablebackpacks:backpack/default can be overridden.

Is this what you meant?

That's exactly what I meant, good stuff.
My bad for missing that.

No worries. Happens to everyone :)