At balance the 1 mA tail current gives about 0.5 mA per transistor. With 20 kOhm collector loads, the nominal collector voltage is about 2 V. The feedback divider uses a -0.5 V reference so FB is near 0 V when OUT is near 2 V: FB = 0.2*OUT + 0.8*(-0.5). Small-signal beta is still 0.2, so the ideal closed-loop non-inverting gain is 5 V/V. The single-ended differential-pair forward gain is finite, so expect slightly less than 5. Change BF or VAF in QN_COURSE and observe that closed-loop gain moves much less than the transistor forward gain.
