There is no passive compression
I'm not sure what you mean by the term. The inlet increases pressure from an ambient of .4 PSI at 80,000, feet to 18 PSI.
I think there may be a little disconnect in thought as to what constitutes a ramjet.
Taking the engine in isolation does not a partial ramjet make. Asking if a TF30 is a ramjet, the answer is no, though could be if the correct inlet was attached, all other things being considered equal (engine metallurgy etc).
For a ramjet to begin operation, the vehicle has to be accelerated to a speed where the inlet will "start". On the SR-71 the inlet will "start" between 1.6 and 1.8 Mach usually. This is when the normal shock moves from the front of the inlet to a position near the shock trap bleed in the throat.
When above Mach 1.6 the spike will retract approx 1-5/8 inches per 0.1 Mach number. Total motion is approx 26 inches. This increases the captured stream tube area 112%, from 8.7 square feet to 18.5 square feet. The throat closes down to 4.16 square feet, 54% of the area t Mach 1.6.
Have read, starting at page 21 of
http://ftp.rta.nato.int/public//PubF...AVT-185-05.pdf