Can you post photographs, please ?
Here are some terms that are important to any discussion on thermostats:
High flow vs. regular flow thermostat
Perhaps this is what you are referencing with your term “orifice” ?
Brass engine block restrictor plate
Or is this what you are referring to as an “orifice” ?
thermostat “piston “ “hat”
This is not designed to totally block coolant flow when it fully expands in to the restrictor plate.
Rated opening temperature
IMHO, your 160° Is too low