I don't understand deep space tracking systems. All it tells me is what "level" it is, saying nothing about the range it covers.
The "Level" is flatly the amount of Deep Space Tracking Stations on a planetary body. What you want to look at is the "Strength" number next to the title of the Deep Space Tracking Station, which says how strongly your DSTS acts as a passive sensor for thermals and EM, equivalent to ship-based systems. Considering that it stacks, and increments in the hundreds, DSTSs are actually extremely powerful compared to shipboard sensors, and can be much better for monitoring points and systems than scoutships if a system body is in the right spot.
Now, for how far a particular "strength" can see sensor contacts, for every single point of sensetivity, the sensor can see a strength 1,000 contact out to 1 million kilometers, with everything being linear, I think.
So a Sensitivity 20 sensor will see a 1,000 strength contact out to 20 million kilometers, a sensitivity 250 sensor would see said contact out to 250 million kilometers instead, etc.
I'm 99% sure that a contact half as large (so 500) will be seen at half the range, and a contact twice the size (2,000) would be seen at double the range, but don't quote me on that one.
If you want an actual view of how far your sensors see things, check out this tab on the system map...
When checked off, it traces circles on the map, such that the circles represent the range your sensor see a particular strength signature out to, the strength in particular being the one you've set with the sliders in the Passive Sensor Ranges tab. Do note that such circles may often be bigger or smaller than visible at your current zoom level.