Rather than lower the dose, I would try to leave the lotion on the scalp for less time. leave it just a little while to make its anti-androgen effect and then remove it from your scalp.
If you leave it working for hours, at the end part of the substance will end up entering the body and that is when the problems come. I think It is not necessary, even a simple shampoo like ketoconazole 2% has been proven to have some anti androgen effect and we only let it act for a few minutes on the head.
I remember there was a guy who would upload videos on YouTube of himself applying Minoxidil foam, which he would leave on his scalp for only a short time and still had very good results for a while.