currently, this plugin is a global damage modifier for all building parts and doors.
no option to specify just door and what is modified for just a door type.

example. if you change bullet to 0.5, all building parts and doors will take half bullet damage.

Now, my other plugin, Damage Mod : Building Blocks.. you can specify which part takes damage or not.

And it does have a percentage damage scale, but it does apply to all parts that have damage blocked.
example. setting protection scale to 50%, and having walls and doors set to true to block damage, doors and walls would  take 50% less damage. all others would not be effected.