16 moms seems an OK dose to me if required.
If 8mgms was not lowering the BP satisfactorily then that would be an indication to raise the dose.
Not my idea of management of high BP but that is a personal opinion.
I've been taking Adizem 300mg for many years now, but it still wasn't enough to take my BP down to the desired level, so they added in 5mg Ramipril, which did the trick.
You will be started on an initial dose, then depending on how that affects your high BP you will be gradually given an increased dose if necessary to reach an optimum maintenance dose.