Too much headspace??

The attached picture is a 5gal carboy of traditional mead. I've racked twice in the last couple months, and lost a bit of product. Is this too much headspace? Should I be worried about oxidation? I'd top it up, but I have nothing to top it up with. And I don't want to add that much water and dilute it.

Also if anyone could comment on the clarity I would really appreciate it. This is my first attempt at mead, and this has been clearing for over 3 months now. Any idea how much clearer it should get and how long it should take?

It's a bit much headspace. I would consider dropping a couple pounds of boiled and cooled glass marbles to bring up the level. And that hasn't dropped clear yet. Mead will drop extremely clear when it's done, you'll almost be able to read newsprint through the fermenter. You can use Sparkelloid or another clarifier to speed up the process.

+1 on the clearing. It seems like it should be more clear than that by now. Did you use anything besides honey? If you've added any type of fruit, you'll probably want to throw a bit of pectic enzyme in there, if not, then I'm not sure why it's not clearer. I like the marbles idea, but that is a lot of space to fill with marbles. If you try it, be cautious about moving it after you've added them. If you move those marbles, it will stir up the stuff on the bottom pretty quickly. I would be tempted to buy a 3 gallon carboy and a 1 gallon jug, and split the batch. If you have to rack again, which you most assuredly will, you'll have the 1 gallon to continuously top off with. Bonus, it will give you an additional empty carboy to fill.

Yeah that's probably a better way to go. It is a lot of headspace.