I would say that there are 2 types of diffuse thinning. one that can be due to stress, illness. medication or diet ect, If you have that type of hairloss you can thin anywhere on your head, above one ear for example. But this thinning will reverse itself with time.
There is also a male pattern baldness diffuse thinning, thats when you thin all over the top of your head but your hairline is more or less intact. If you have this kind of thinning you should use the standard treatments (finasteride/MIN/nizoral)