Persistent Spell: What's up with Fixed Range?

[Urpriest]

Persistent Spell can only be used on Personal or Fixed-Range spells.

Personal makes some amount of sense: the spell is limited to work only on the caster, so it's got to be a buff of some sort, and a buff that can only be applied to a single person at that, which limits applicability.

Fixed-Range, on the other hand, makes zero sense. Fixed-Range spells are those with a range that doesn't scale with caster level. There isn't some sort of guiding principle that makes spells Fixed-Range or not. Rather, Fixed-Range spells are spells that, for one reason or another, happened to be a shape that shouldn't scale with caster level. That's...it.

Does anyone care to speculate on the designer intent here? What common property of Fixed-Range spells did the designers think existed in order to justify their inclusion in this feat?

[NeoPhoenix0]

I don't think they thought. I think they wanted to have detect magic persistable because it is similar to personal spells and left it at that.

[Douglas]

Does anyone care to speculate on the designer intent here? What common property of Fixed-Range spells did the designers think existed in order to justify their inclusion in this feat?
My guess is that all the examples they knew of were the detect spells and maybe a few auras. To properly match that intent, if that's what they were going for, a better wording word be "personal spells, or area spells that emanate from the caster".