Magnus is absolutely not going to explain, because it's Alex's business that Alex hates gods even more than Magnus does, with good reason, and so the fact that she likes Sif is the biggest and ringingest of all possible endorsements. He says, "But yeah. The rest of them are pretty hit-or-miss. Mostly miss. I guess my grandpappy is okay." He's actually answered at least one of Magnus's prayers to his dad. "But I'm pretty sure he has a foot fetish. But, like, only for his own feet."