First observed in a matchmade game with my back to the crates, reproduced in hero sandbox. It looks like any closer than a body width away from a crate will cause the owl to detonate immediately on cast when facing away from the crate.
Standing at the very limit of this radius makes it so the owl only detonates immediately when facing directly away from the crate or when the crate is on the character's right side. Aiming so the crate is on the character's left side stops the immediate detonation, even when the character is touching the crate. Similar things happen when standing near enemy heroes or target dummies.
It only happens to smaller objects (destructible gold figurines, enemy candle troopers) when they are on the character's right side.
TLDR: it looks like Grey Talon's ult originates somewhere over/behind his right shoulder and collides with things he does not collide with himself.
Standing at the very limit of this radius makes it so the owl only detonates immediately when facing directly away from the crate or when the crate is on the character's right side. Aiming so the crate is on the character's left side stops the immediate detonation, even when the character is touching the crate. Similar things happen when standing near enemy heroes or target dummies.
It only happens to smaller objects (destructible gold figurines, enemy candle troopers) when they are on the character's right side.
TLDR: it looks like Grey Talon's ult originates somewhere over/behind his right shoulder and collides with things he does not collide with himself.