This is what I've found on wiki:
"After birth, the 5α-R1 is expressed in more locations, including the liver, skin, scalp and prostate. 5α-R2 is expressed in prostate, seminal vesicles, epididymis liver, and to a lesser extent the scalp and skin. Hepatic expression of both 5α-R1 and 2 is immediate, but disappears in the skin and scalp at month 18. Then, at puberty, only 5α-R1 is reexpressed in the skin and scalp."
https://www.jstage.jst.go.jp/article/antibiotics1968/43/12/43_12_1615/_article
Among the inhibitors of 5α-R1 are zinc and linoleic-acid. You can find these supplements in any vitamin store. If you are on finasteride, I WOULD NOT REPLACE IT WITH SUPPLEMENTS. I'm not saying it wouldn't work, but there is enough research to gauge the efficacy of taking natural supplements to inhibit 5α-R1 expressions in hair follicles. It wouldnt hurt to incorporate these into your regimen though. I will add this though: I've suffered from moderate acne-breakouts and after taking zinc religiously for three weeks, my break-outs have considerably reduced. I only get a pimple or two every couple weeks now.
EDIT: finasteride has been clinically proven to treat male pattern baldness. This corresponds to male pattern baldness's physiology because finasteride also inhibits 5α-R1 albeit less effectively than 5α-R2. This may explain why some finasteride users continue to lose hair, or don't respond at all because the drug itself is not able to effectively inhibit 5α-R1 for that individual. In which case, hair loss progresses because the scalp contains more 5α-R1 expressions in the scalp than 5α-R2. I'm not an expert in this field, so take everything I said with a grain of salt.
EDIT2: You said you are taking castor oil orally and have been getting good results? How so? Did shedding decrease? Does castor oil reduce DHT? Also, how long have you been tking minoxidil? Some people don't see results until a year later.