Where does a Siamese usually sleep when it insists on being a velcro cat but hates closed doors?

You're missing the point entirely. A Siamese that hates closed doors will sleep right outside your bedroom door, plastered against the crack where the draft comes through, because they can still hear you. The fix is to leave the door cracked open just a few inches. That way, they can shove their nose through to check on you while still technically being "in" the same space, and they'll curl up right there on the threshold.

My Siamese claimed the exact spot where the hallway carpet meets the bathroom tile, right against the doorjamb. She'd stretch out with one paw actually touching the bottom of the closed door, as if that contact somehow kept her connected to me. I eventually gave up and put a plush bed right there, which she ignores in favor of the bare floor. The real trick is leaving a closet door slightly ajar so she can burrow into a hanging sweater while still hearing every sound from the room I'm in.

Mine claimed the top of the bookshelf in the hallway, right where she could see every door in the house without being near any of them. Back in the old days, a cat like that would've just followed you from room to room all day, but now they've figured out they can supervise from a single strategic perch. She'd sprawl there with one eye on the bedroom door and the other on the bathroom, only descending when she heard the doorknob turn.

Right outside the bathroom door, sprawled dramatically across the bathmat with one paw shoved under the gap. She'd rather endure the cold tile floor than risk being separated from me by a shut door, but the moment I cracked it open even an inch, she'd snake her whole body through and curl up on my feet. I ended up buying a cheap cushioned mat just for that spot, because she refused to move.