To the best of my knowledge, the ASI is not calibrated to take compressibility into account.
This is the reason we have EAS. in the first place.
When dealing with ASI keep in mind it is just a simple pressure gauge. Someone just put knots on the scale in stead of pressure..Simply speaking the ASI will measure the pressure difference between total and static pressure and it cannot deal with compressed air, and some idiot labelled the scale with knots in stead of pascal..
The next problem is then if you fly fast or high the air gets compressed in the pitot tube and all pressure measures goes down the drain.
In order to figure out what dynamic pressure the plane is actually subject to EAS was "invented". If we could measure the pressure the plane was subject to in the flying high/fast scenario, we could convert that pressure into a true airspeed equivalent..So we measure the pressure At some altitude. We then imagine that we where flying at sea level on a standard day and figure out what speed we had to fly to get the same pressure. This speed is EAS. If the pressure in the pitot tube was incompressible, TAS. and EAS would always be equal.