Radu Pierces invisibility.

[TorkaUmbra]

It's just a lot of assuming really and overall none of this is worth overthinking, I understand threads like this can be made due to the frustration of not being able to be in the outskirts as a high OCR character, but presuming this and that doesn't add anything or help solve the big mystery.

If I were to use the process of elimination I would consider the likelihood of some invisible mage using mass see invis and Radu happened to be in the range, because people buff behind that house all the time. At the end of the day no serious issue happened and if the staff wants to make a new rule clarification they can, that's S+.

impossible that it was on accident. Mass see invis is a short Aoe. Also...who would ward near the outskirts where radu and garda are able to see?
it had to be a potion.

[SardineTheAncestor]

Behind that house is well out of line of sight of him or any guards. It's a popular spot to hang around, and it could reach Radu from there.

The ranges listed are very different from what they are in practice. Mass Spell Resistance basically requires you to be touching the caster and is listed as medium. Mass See Invis has a slightly shorter range than Prayer which is listed as colossal.