Beginner EQ Question (rolling off lows)

Let me preference this by saying I realize that you need to use your ears rather than rely on visuals to mix.

That said, when people say you should roll off lower frequencies (under 100Hz for example) from any instruments that may interfere with your bass, are they referring to where the curve begins or the frequency setting itself?

In the screenshot below, I've set the frequency to 100Hz & the slope to 24db/Oct. Of course the curve starts at 100Hz but appears to be eliminating lower frequencies primarily around just under 50Hz.

In this case, represented by the low-cut shown in red, should I consider increasing the frequency so that the red shade is closer to 100Hz on the X/Y - so that the curve begins to slope at around 230Hz?

So ultimately, I have a synth part that has low frequencies below 100Hz that I'd like to eliminate to make room for the bass.

Also, any insight into slope settings or guidance in general would be appreciated.

Thanks in advance!