Greetings and Salutations. Well, in the case of the natural ability, I would say they could stack. Though I think you can only have one enhancement (from an outside source). So spells, psionics, magical item, etc. would overlap with each other. So if you had the ability from a Rune Sword, then cast Spell, then used a Psionic, it would still be just 1/2 (overlap). However, with a natural ability, I view it a bit different. That person's body just works differently. Now, granted, if you said the resistance was because of a magical nature you could still have a good point (to overlap), but I feel it could just as easily be some type of physical component, like natural insulation, skin/hide is made of naturally resistant materials, etc. There are real life fire resistant items for instance. Because this is "natural" it can still be enhanced by a spell, psionic, etc. Therefore, in the case of a "natural" resistance, when amplified by an enhancement it would stack, reducing it to 1/4 damage. I know that would complicate the rule a bit, but that's how I personally would rule it. It's what makes sense to me at least, others are free to disagree. Thank you for your time and patience, please have a nice day. Farewell and safe journeys to all.
P.S. I used the example of fire given, but for the record I would follow the rule in general. Natural + Enhancement = Stack, Enhancement + Enhancement = Overlap.
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