Not sure to as why my simulation values are different to my calculated values for voltage across certain nodes
Since you're already adding an op amp buffer, might as well use the second out of a dual pack and make this analysis much simpler.







simulate this circuit &ndash; Schematic created using CircuitLab

Rearranging the circuit and adding the second buffer removes the dependencies between the filter and scaling. The high pass corner frequency is still dependent on the LM386 input impedance. As it it will be ~30Hz. If that's a problem, 1uF will get it down to 3Hz.