The nether brick to smooth nether brick smelting recipe conflicts with the vanilla nether brick to cracked nether brick smelting recipe, which means that the player needs a mod like Polymorph to access both blocks. In my testing, smooth nether bricks were favoured. Might I suggest making smooth nether bricks craftable or stonecuttable and removing the smelting recipe so that cracked nether bricks can still be obtained?