As I understand it (from googling) the difference between a BiPap & a Cpap is that a Bipap reduces pressure as the the user breathes out. Also the Bipap is more expensive. Online explanations state that Cpap pressure remains constant when both breathing in & out.

I have been using a Cpap machine for over 5 years now & it can be set to reduce pressure when I breathe out - So how can this be? Perhaps a Bipap has greater adjustability?
Whilst I can reduce the pressure for breathing out, & the timing of this in the settings, I think it is limited to 3cmH2O below the breathing in pressure.

If a reduction of 3cmH2O pressure were sufficient you may not need to spend so much. ??