Nerra reflecting spell resistance

[Nikker]

Hello everyone, I'm playing 3.5 and I need help to understand something about the Nerra.
I'll quote from Fiend Folio:

Reflective Spell Resistance (Sp): A nerra has a special type of spell resistance that causes any targeted spell it successfully resists to bounce off and reflect back at the caster. The caster becomes either the spell's target or the point of origin for the spell's effect, as appropriate. In addition, nerras are immune to gaze attacks, and such an effect is reflected back to its origin.

Now, it looks like a Varoot (a subrace of Nerra) has a fixed SR of 13; what happens if I somewhat manage to improve their SR? Like with a Daazzix's Vest?
Does the reflective property apply to the whole SR 18? Only to SR 13? Is it an ability that Nerra "add" to their SR due to being mirror-like?

Does the reflective SR depends on the Nerra being mirror-like? What if it wear clothes? What if the Nerra is under an illusion spell looking like something else? (For example if the Varoon is using their Change self spell-like ability, which should be Disguise self in 3.5 if I'm not wrong)

Thank you in advance for the insight.

[Silva Stormrage]

Any spell resistance the Nerra has is the reflective type. Even if a cleric were to cast the spell "Spell Resistance" and granted the Nerra a much higher spell resistance value the Nerra would still reflect any spells that failed to beat SR. The ability to reflect spells is a Spell Like ability that the Nerra has, it isn't tied to any particular value of spell resistance it simply modifies any SR that the Nerra has. It also wouldn't change if the Nerra was disguised or covered in some way.

[Fouredged Sword]

Yeah. Nerra don't actually have different spell resistance.

They have normal spell resistance and then a special quality that causes any spell that is negated by their spell resistance to be reversed.

These are two different things. They exist independently of one another.