There aren't many pictures of saddled snow-unicorns, but the ones there are show the saddles really far forward, pretty much at the base of the neck. I think the theory is they're so huge, there's room for a whole lot of gear behind the saddle. See this picture and this picture. (In the second one, the humans are all kids, thus the scaling.)

This is just the sketch stage, but they don't have whiskers -- not that all the pictures of them do.

I like the range and perspective on the second one. You're going to color that one, I hope? I think that'd give it depth that might be hard to capture with just linework.