I’ve had the same question about smaller bones scoring lower numbers. This article says they’ve decided it doesn’t matter much (looks at men’s and women’s bone) when considering fracture risk.
Using the Same Bone Density Reference Database for Men and Women Provides a Simpler Estimation of Fracture Risk
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5101072/
The International Atomic Energy Agency has a publication all about the DXA bone scan:
https://www-pub.iaea.org/MTCD/Publications/PDF/Pub1479_web.pdf
This states that there are definite differences in the size and bone density of men and women and some populations, Asian is mentioned. It says that DXA looks at only 2 parameters and cannot determine a difference between a thicker less-dense bone and a thinner high-density bone.
It also states there can be about an 8% difference in scores from different machines.

I’ve felt unsure of my DXA scores as I have smaller wrist bones than many women of my height. Also because I don’t know anyone who has broken their hip, I’m 70 yo. My mother (osteoporosis) and 2 older sisters (both with osteopenia) have never broken a hip. Although my mother had some compression spinal fractures in her later years.

I did finally decide to start bone density treatment - which is a good thing because right at that same time I was diagnosed with breast cancer. Some of the bone density treatments can harden the bone against metastasis (and bone is one of the first places BC will often move to). So I see it doing double duty, increasing bone and deterring cancer.