Figure 6 shows a two-transistor amplifier with a feedback resistor "Rf". This amplifier is often referred to as a "shunt-series feedback" amplifier, and analyzed on the basis that resistor "R2" is in series with the output and samples output current, while "Rf" is in shunt (parallel) with the input and subtracts from the input current. See the article on negative feedback amplifier and references by Meyer or Sedra. That is, the amplifier uses current feedback. It frequently is ambiguous just what type of feedback is involved in an amplifier, and the asymptotic gain approach has the advantage/disadvantage that it works whether or not you understand the circuit.