I needed finer control of Vpp. Since this is an experimental design, I decided to make some calculated guesses to choose the right values.
To start with, I believe that putting a resistor between the emitter and ground of the feedback transistor will limit the gain of the transistor. The voltage of this resistor will rise as the current through it increases limiting the current gain of the circuit. The first guess I tried was calculating the resistor as if the transistor wasn’t there(same as fully saturated) for my max voltage (25 V).