The charcoal piles in forestry currently clamp the value of walls (including when set manually via crafttweaker scripts) to a range between amount.base and 63 - amount.base. This causes charcoal piles to be unable to produce less than double that config, as a normal value like 5 will get clamped up to the config.

The default config value is 8, so currently all forestry charcoal piles return 16 charcoal per pile as all default walls have an increase of less than 8 so are being clamped.

Error is present in 383 of Forestry from curseforge.