THC advice please

Hi All,
I need to cut thin plate, 1.6.mm, on my plasma table. I am using a floating head on the Z axes. The issue is when the torch lowers it deflects the plate before triggering the switch, resulting in issues. . I was thinking of using a proximity switch close to the plasma head but am concerned that the switch will get damaged. So i thought of using a pencil pneumatic cylinder with the sensor on the end of it so that when establishing the initial height the cylinder would extend and then retract after the height is sensed.. I would prefer a custom post processor as editing the gcode would become quiet time consuming. Does anyone have any input to a ) a better idea or b) point me in the right direction for the post. I am currently using Sheetcam and mach 3. My THC does not support Ohmic sensing. .

I use a limit switch that is lowered via an air solenoid and it works well. I have a macro in Mach to do the required move, fire solenoid, move axis etc. I then have my post processor (Fusion) call an M code to do the deed.