I have a question on Type II compensator shown in this document SLVA662 page 4. https://www.ti.com/lit/an/slva662/slva662.pdf?ts=1641427694852&ref_url=https%253A%252F%252Fwww.google.co.kr%252F
it mentions 'the transfer function is obtained by calculating the impedance offered by the network placed in the Op-Amp feedback path (Zf) and dividing it by the upper resistor (R1)'.
R4 is not part of this transfer function,. Is this because in AC small signal mode, the node highlight in red is equivalent to shorted to ground and R4 shorted out ?
thanks for your help in advance,