This debate has been going on for years. The misconception is that since nandrolone tends to have a lower androgenic profile, its easier on hair. That is true but unmetabolized nandrolone is a very strong binder and activator of androgen receptors - stronger than testosterone and on a level close to DHT. You can look that up if you want, but its true. When people talk about the A:A Profile of Deca, they are talking about metabolized.
This is the issue; hypothetically finasteride blocks the 5AR action/conversion with nandrolone resulting in circulating hormone that has more affinity to the AR then metabolized nandrolone - being WORSE at the AR site (i.e. hair follicles).