I love how this challenge is making all the different versions of Severus *sigh* so clear. Yours is so much more Slytherin than mine and I love him for it. I love seeing him use his cleverness and cunning to help his lover and get what he wants.
And I actually agree with you that Severus would be much more likely to have a relationship with Lucius than Harry. I just can't write Lucius at all and, no offense, but I just don't really like him. *shrug* But I do think it makes sense and you've written it wonderfully.