"Full powered" implies "irreversible", which implies that all stick-feel is artificial, and there is no elevator force feedback to the stick. In that case I'd expect the elevator to be only a function of stick position in a system fitted with a trim tab. A conventional lgiht aircraft (say PA28) system is reversible and thus elevator would be displaced.
But, for this very reason I'd not expect a trim tab in a system with irreversible controls. I'd expect the cockpit trim control to be deflecting the neutral elevator setting in some way, and would be very surprised to see a trim-tab.
Is there any actual aircraft out there with fully powered controls and a trim tab in the same circuit? If there is, it is likely to be low-powered, and operating in the opposite sense to the trim-tab in a reversible control system.
G