User blog comment:KnocknickKnock/9 gates + master of the celestial realm/@comment-24066070-20131208182752/@comment-7418318-20131214215857

That's what I meant by it being relegated to surprise attack and sniping from a distance.

But regarding the other part of your comment: I wouldn't be so sure about Caelum really being so passive. Remember that Angel didn't treat her spirits well, so it wouldn't be too surprising if Caelum just did as little as he could get away with, without breaking the laws of spirits.

After all his last attack went around Lucy. While in the manga Angel said "I missed", in the anime Angel's looked angrily at Caelum saying "You too?" indicating strongly that the spirit sabotaged her efforts in an act of rebellion (considering how the shot curved around Lucy, rather than just going wide, that might still have happened in the manga too, but without Angel realizing it, though there's no confirmation either way). If Caelum was used by someone who treats it with respect, it might be a bit more active.

Even though it's an anime-only filler arc, there's also that one scene in the KotSS arc, where Caelum automatically shoots at Racer the moment he appears (though it misses). That might have been because Katja ordered it to "keep watch", or it might have been due to Katja being a good master, unlike Angel.