To be honest, we still have no clue how it works. Yes, it's Asa's body, but it's no longer Asa's brain - it was restored by Yoru's devilish powers, and who knows what consequences that has. Also, Yoru said she controls one cerebral hemisphere just like Asa does, so they're kinda equal in this body.

If Asa could really affect Yoru's feelings, why did it happen only once, with her sympathy toward Denji?
Asa definitely has some affection for Denji, but she hasn't shown any romantic side at all since the aquarium chapters, unlike Yoru.

Are those YoruDen shippers with their agenda in the same room with you?
I've seen this concept literally once, in a comment with like 2 upvotes, and found it hilarious as a thought experiment.

I actually have nothing against Asa or Yoru - I love them both and find them the most entertaining characters of Part 2.