I just wanna make sure that I understand the plugin right.

If a multiplier as set to 0 this will never decay no matter requireCupboard set to true?
If multiplier 1 it will decay if not in cupboard range then?

Or is it like all multipliers are connected only to requireCupboard if set to true and if false its globally?

I wonder. I have requireCupboard set to true and twigs 1.0.
Why do twigs inside and outside of cupboard range decay?
I thought the requireCupboard option is to prevent any decay in cupboard range.
Otherwise this option wouldn't have any sense, right?

requireCupboard true:
 We check for an attached cupboard to determine whether or not a building will decay based on our configuration (multipliers).  This includes twig.  Without a cupboard, the building will decay normally due to upkeep requirements in Rust as if the plugin were not installed.

requireCupboard false:
 We skip the check for a cupboard and process building damage anyway using the plugin configuration.

Basically, all it is is a check for the admin whether to require a cupboard to prevent or adjust decay based on the configuration for block grade multipliers (twig/wood/stone/etc.)  In the older versions of the plugin before this check, people would regularly place foundations in the wild as teleport points, and they might have lasted quite a while, even with decay.

It is possible that another plugin is impacting decay as well.  Many plugins call the same function, OnEntityTakeDamage().

Finally, a multiplier of 0 is required to prevent decay.  It is literally normal decay * multiplier.  If 1, normal decay.  Anything less, less decay than normal.  0, no decay.