This is from your post #14, showing r2 being factored out of the expression for t;
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r2 is involved in the 180 degree phase change, but its effect doesn't change with frequency, so the frequency of oscillation of the circuit won't depend on r2. Whether it oscillates at all will depend on r2, but not the actual frequency of oscillation.
Let's choose some values for components and plot the magnitude and angle of t. Let r=1000 ohms, c=.01 uF, and r2 = 8000 ohms for the blue plot, r2 = 16000 ohms for the red plot.
The magnitude changes when r2 changes from 8000 to 16000 ohms, but the phase angle does not change; the red and blue plots of phase are on top of each other:
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