Is it possible to have mid 90's psi when cold and 70 psi after warm up?

 

Check your RPM's/voltage and see if they're the same. Starter may not turn the same RPM's warm vs cold.

It is still possible to have a large drop hot vs cold but start simple first.

 

Make sure you are cranking and holding the throttle wide open for a correct reading.

When cold the thermowax will hold the throttle plates partially open for you as well as the BAC will bypass more air and improve the reading, with the engine warmed the throttle plates will be all the way closed and the BAC will be closed down resulting in a lower compression reading.