This question highlights an often overlooked concern when using pressure sensors mounted underneath ejector pins.
How much of a gap should be used between the pressure sensor and the ejector pin?
The general recommendation from most manufacturers is between 0.25-0.5mm or 0.010-0.020in.
In reality, this specification refers to the clearance between the top of the ejector pin head and the counter-bore in the ejector plate. Most mold makers use a similar ejector pin clearance even when a sensor is not being used.
The purpose of this clearance is to ensure there is no preload on the sensor, especially if any dirt gets beneath the sensor. Such a preload will destroy the sensor and provide erroneous pressure readings.