the basis is the potency of pyrilutamide. think of it like magnets, pyrilutamide is a pole and the androgen receptor is a pole. since the attraction is so high the hope is that most of the drug binds the receptors in the scalp so less can go systemic. thats why a small percentage solution is used. with a weaker AA you use more but the chance it "misses" a scalp receptor and goes into the blood is higher. additionally its that it becomes a weaker metabolite once it reaches the serum and that in low concentration. however unlike CB or topicalutamide not much thought has gone into it in my opinion and I never understood why they think it is better in terms of sexual side effects than finasteride. because it is not a smart designed drug. as to your other questions:
no, firstly a DHT receptor is not a thing, DHT like other androgens binds the androgen receptor. they have the same DNA throughout the body and this the same structure. otherwise imagine, a testosterone molecule in the muscle cells could not bind to the receptor in the penis, that'd be weird because then you'd have to have different kinds of testosterone too.
yes there should be no imbalance. thats not needed though, if you take a strong oral anti androgen your >DHT will also not change(aside from homeostasis) however what can give sides on this drug is that it binds to the receptor T or DHT would normally bind to and NOT just in the scalp. in that case, Kintor is majorly fucked as that makes pyrilutamid a worse drug overall than finasteride in every aspect. it is also saver to reduce DHT which only acts in certain tissues than to take a receptor antagonist which acts in ALL tissues where any androgenic action takes place. the brain, penis, and in contrast to DHT the muscles, the bone, other organs, that'd be pretty bad. they certainly could not deliver this for kids with acne then. also their major marketing point would be destroyed. so either it gives sexual sides or not, the debate will I think not be settled before the phase 3 results come out