Make sure the neckline is cut straight, same with the side burn area, that's a very important part of a masculine haircut that I don't see often in "butch cuts".
I'm in the same boat, round faced part asian, round cheeks and a tiny chin are hard to make look masculine. My hair is (very bleached) platinum blonde, shaggy, short on the sides (1in) and slightly long on top (almost goes over my eyes in the front, 4-5in) with straight cut side burns and back, I pass sometimes but mostly my voice gives it away. I use to have a mohawk but since I don't have a masculine hairline, I actually passed less with that then I do with my shaggy hair.
If you have a feminine hairline, you can always shave it to a more masculine shape. As long as you maintain it, it looks good, I've seen it done a few times pretty successfully. It REALLY helps with passing, more than you'd think!