RDR-4B Wx Rdr Interpretation

[extricate]

Hi there,

I'm looking through the RDR-4B manual. Any idea what does the graphic below mean? Does it mean if the range is set at 20nm, the radar will look down 6,900ft below?

Side question: How do I understand the link between radar tilt and range? Am I right to think in terms of trigo? Say i'm at 40nm, if my tilt is 2 deg down, wx radar is scanning 8,487ft down? If I set it at 80nm, wx radar is scanning more downwards? And how do I operationalise this in real wx ops?

Thanks