Perhaps we might want a little bit more explanation about this?
Maybe just the full text instead of the abbreviation?

We can do a better message, but out of curiosity why is the nearly identical "Post response URL" above any less informative? It seems to me that Logout URL and Post URL only have meaning if you already have a familiarity with SAML profiles. How does this sound as a reworded help message?

PAOS response URL, used for ECP.

We can't spell out PAOS because it's not an acronym, it's stands for "reverse soap" with soap spelled backwards, I don't really see how adding that tidbit adds much to the help message, likewise how does spelling out ECP as "Enhanced Client & Proxy" help? Either you know what this stuff is or you don't

The main issue I had was that "PAOS" sounds like it's an abbreviation, and I kept trying to think up what it could be to think if I would know what it means.
The Logout URL and Post URL don't sound like abbreviations, which makes me not even try to parse them if I have never heard of them before.

The rewording you suggest sounds reasonable, but we could also just lowercase "paos".

Looks good to me