Sure there may be some multiple variants of SRS circuit tuning, for the circuit in Atlas book, in staring mode the voltage on the primary winding is just 40V so apparent 'resonance' is really weak. BUT if you look at vector diagram you'll see the voltage at choke winding and at capacitor is in-phase, which should not be a case for a series resonant LC tank. So may be a better model for the circuit will be a step-up auto-transformer (fed by a capacitor current) made from primary and secondary windings unbalance?

That is indeed how i imagine it. There is (unbalance L) + C series circuit, which does not have to be in resonance but to pass the desired current for filament heating. Then the rest of the winding steps up the voltage

The phase diagram may vary somewhat between manufacturers - Eltam use a different capacitor value than UK manufacturers. Also, i have seen moderate++ success with Eltam ballasts starting 36W T8's, something which is not supposed to work according to descriptions by UK users

Would definitely like to dig up mine and provide here whats possible