I feel that what makes it look more like soap bubbles is the size of the bubbles. A proper head is a smooth foam that is comprised of tiny tiny bubbles, so I feel that the top should look smooth (a flat line) rather than bubbling over the way you have it. Also as others have mentioned, filling the beer portion with bubbles will also make it look more like you want it to look!
Edit: The bottom option that you originally posted is more what I'm talking about, but if you make a gradient that's darker towards the head and lighter closer to the bottom, it would look more realistic