Florinef thou its helped my POTS a bit (still got a way to go there), it didnt help my orthostatic hypertension. Im currently trailing Clonidine for that which "may" be helping it (I havent spotted a very high BP reading yet while Ive been trialing it).
It does make sense thou that it could help the orthostatic hypertension thou in some due to it raising blood volume cause low blood volume causes this issue for some. Dr David Bell has treated some of his orthostatic hypertension patients with IV saline to bring down their BP.
I guess you can tell if its being caused by low blood volume if those things which help low blood volume help it.
You may also have other signs of low blood volume eg thirsty a lot and needing to drink more then most people, peeing heaps, dizzy when just standing (which may be better when moving .. indicates of lack of blood getting to brain when standing and hence often low blood volume).