>>16707651 (OP)There is a concept in pharmacology called "volume of distribution", look it up.
The effects of testosterone (or any other hormone) depend on its concentration in the blood and its receptor and downstream pathways, but there are several points to consider here:
1-Testosterone is fat soluble:
People with more fat have a larger volume of distribution for testosterone, so if you give the same dose of testosterone to two people, one thin and one obese, the thin person will have higher blood concentrations than the obese person. This is because testosterone is sequestered in fat tissue so its effective concentration in the blood decreases.
2-Testosterone is protein bound:
Testosterone does not exist as free hormone in the blood, instead about 54% of testosterone is bound to albumin while about 44% is bound to a protein called sex-hormone binding globulin (SHBG) and only about 2% is actually free and non-bound. Protein bound testosterone is not active, it is only the free testosterone which can exert physiologic effects. Variations in SHBG concentrations will affect the volume of distribution of testosterone (and also estradiol for that matter) and subsequently its serum concentrations.
3-Testosterone effects depend on its receptor:
Finally, even if you have the right concentrations, the end result will be determined by the androgen receptor and its downstream pathways which is mostly determined by genetics. So people with the exact same serum concentrations might have different responses.
4-Testosterone effects are regulated:
This is done by the Hypothalamus, Pituitary and Testis. If you have naturally low testosterone concentration without symptoms then it means that your androgen receptors are more sensitive to testosterone, conversely someone with high levels of testosterone (but again, no symptoms) might actually have lowered sensitivity to it.
TL;DR It depends on fatness, SHBG and genetics, not just body size.