I find it interesting that some people's bodies can simply store fat in more uncommon patterns. I have a female comeptitor I'm working with now who is a good 8 weeks out from her show, with shredded abs, cuts in her upper legs, and yet soft looking arms.
What I find myself coming back to, and I don't know if there's truly any scientific evidence to support this or not, is something an old college professor said to me. Basically it was his thinking that your body will naturally lose bodyfat in the reverse order that it was put on initially. Now where your body packs it on is genetic as far as I know, and I can personally attest to seeing this pattern of loss in myself and other competitors as well. I'd be a month or so out from a contest, upper body shredded to hell (veins running through my abs, my obliques, even some feather in my back -as creepy as that sounds), and yet my lower body (legs, glutes) were still fairly smooth from remaining bodyfat.
When you say that you're 10%, and I mean this as objectively and nicely as I can put it, are you seriously 10%, or just guessing, using a handheld bf tester, or even some plastic calipers? I ask because the amount of people who claim 10%, and the amount of people who truly are (and understand what it looks like) is a vastly different figure. Also, as you alluded to, increasing muscle mass will always be helpful in creating a look of more definition. Just think about it, more muscular bulk pushing out and stretching against your skin, of course it will help