b377
I think you will find that because the engine's compressor can only handle incoming air at subsonic speeds ,then when the aircraft is at Mach 2.0 the 14 ft long intake has to slow the air down in rough figues from 1350 mph to
350 mph .
As the figure in your web site shows it does this by creating a number of shock waves in the forward part of the intake with the last shock wave[ where the air goes from supersonic to subsonic] being between the two intake ramps
In slowing the air down it also increases it's pressure , and I think the compression ratio was 7 to 1 but could be wrong. This was like having another compressor on the front of the engine with no need for turbine at the back
You can think of it like a piston engine with a turbo charger in the air intake so making the engine more powerful because it pre- compressed the air for the engine
Hope it helps