I use the HU to minimize the built in car speakers bass, and the bass knob to control the sub's output. letting the sub pretty much handle most of the bass. the HU bass control also alters the sub, that's where the knob comes into play.
I just got a 2026 Base GT(non-Vert). and also just had a sub and amp installed. I also installed a bass control knob. I notice when driving between 2k-3k maybe a little higher, I can hear the bass rumbling. most noticeable like when you are going a shift higher than the speed you are traveling...