Fig 3 is about right. The green feedback path is usually an N-turn winding to net an N-to-1 current transformer.
There are usually two physical toroids. Ib, If, and T3 are wound on both, as if they were a single core. T1 and T2 are each wound on one of the cores, in opposite directions so that there's no net coupling of the carrier frequency into T3 or the customer's Ib circuit.
The AC path (sense winding T3 and its amplifier, driving If) fight to keep the flux zero at higher frequencies. The second-harmonic system works at low frequencies, again to keep net core flux zero, which happens when Ib = N * If.
I designed one of these once. It was fun, and not all that easy.
John