It's nice to feel wanted!
The operation of the ramps and other systems is well explained in the many books about the SSC so I shall only go into briefest detail here -
The successful design of the ramp control system was the absolute key to Concs success over competing designs.
The ramps' job is to decelerate the airflow so it is subsonic as it reaches the engine. They do this by moving up and down, focussing a succession of shockwaves onto the lower lip of the intake. The passage of the free stream through these shockwaves decelerates it and greatly increases its pressure.
The position of the ramps needs to be adjusted whenever the engine demand changes, the speed changes, the alpha changes or the temp changes. They are controlled normally by dual controllers - the first digital full authority computers ever used in a commercial a/c.
If the shockwaves are focussed aft of the lip the condition is known as 'supercritical'. Efficiency will be reduced in this state (as by a 'subcritical' condition)
I've not read the book but your quote suggests that the ramps did not have enough authority to deal with the upgraded engines at ISA>+5. A problem long since sorted.
Because the engines run, basically, to an RPM in the crz and because, of course, the overriding airframe concerns are mach no. and temperature, the conc is very sensitive to OAT - negative ISA = good, positive ISA bad.
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