u do not "tune" your abc, u tune ur UTEC, the abc is there for fine adjustment
the UTEC is the primary boost control, the abc is just what it stands for the auxilary boost controller.
use ur UTEC to tune to roughly 16psi, then use the abc for fine adjustment.
i.e. you are boosting 15, use the abc to bump it up 1psi. do not use it as a manual boost controller