The bubble butt look comes from a combination of tighter, denser glutes, the pushup effect of the hamstrings, and fat distribution that has less places to go. A taller woman will have the same overall fat % throughout the body as a smaller woman but the height difference changes the distribution and muscle position.
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A taller girl can have a significantly more full ass than a shorter girl since longer leg muscles can support more ass but it requires more muscle development. On a shorter girl the the Gluteus maximus is smaller but also short and more clumped together making it look bigger while on a taller women it's larger but more stretched out due to the longer legs and, a further muscle anchor point from the upper hips to the femurs. The width of the hips also plays a big difference since birthing hips tilt the angle of muscle attachment giving a girl a more full rear.
Take a look at the pictures below, notice how thick the muscles around the femurs are? They are almost as thick as their waists.
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Hamstrings don't just expand outward but slightly upward as they become more developed due to being attached to the top portions of a women's hip bone. The side adductor muscles also fluff up the fat around the front of the thighs which pushes back and together the rear muscles and fat, making a woman's ass rounder.
It's like a push-up bra for the butt-checks but all natural. High heels try to do the same thing by forcing a woman's leg and ass muscles to contract more than at rest; muscle development still works better though and complements the heels effect more.
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Most womens exercise routines focus either on dieting or working out like a man, neither are correct, especially for taller women. Look at the asses of tall girls who play tennis, they are round and correctly proportioned despite the girls being trim.
If you read to the end, congrats, that concludes your gooner biology lesson for the day.
tl;dr: more mass means more ass, most tall women just don't take advantage of it.