I am in a similar situation, perhaps a bit more diffuse than you. I still have hairs on my crown even though they are weak and wispy, but this is the first area I would like to get a transplant on. Im not expecting full coverage as I need to save grafts for the front, but I would just like enough to where if I add concealer, I can pass for "good enough" to the untrained eyes of most people.
However, I'm also worried that a transplant would damage my existing weak hairs, which still provide some, albeit marginal, cosmetic help. So I don't know if I should wait until those fall out, if I should stop applying minoxidil there so I guarantee that they do fall out, or to just get a transplant and hope that they don't. For reference, I've been on finasteride and minoxidil for 3 years already.