It's just that by my estimates, your 16V AC will become approx. 22V DC, drop a couple of volts across the regulator, say leaving approx. 20v.
Regulator will start around 2V out, so 18v adjusted by a 10k pot so maybe 1.8V per turn so after 1 turn approx 4V out....see what I'm getting at?
You said...