I figured it out.
In order for the matrix modulator to properly work I need to set my filter cutoff to 100%.
Then use the "Value" knob in the Matrix Modulator module as the main Filter Cutoff knob.
I was using a 2nd UI knob that I wired to the Cutoff, but the Matrix Mod module expects you to use "Value" as the main knob/slider and "Intensity" as the modulation depth.
Setting the filter to 100% ensure that both "Value" and "Intensity" have control over the full range of the filter.

