How can I isolate altitude as a specific range variable on a Sporty's electronic e6b?
TL;DR; You need to look up the burn rate in your POH.

I think you are misunderstanding the examples...

Your fuel burn rate is determined by your power setting and altitude from your charts in your POH. You need to look that up, so to calculate the range, here is what you do:

First, use your POH to look up your fuel burn for a specific power setting/manifold pressure/altitude, here is an example from a Cessna 172 POH:



You can then you can use that fuel burn rate in your calculations. A range calculation is simply:

$$
Range = {Fuel \above 1pt BurnRate} GS
$$

So using the table above, if we are cruising at 6000 feet @ 2200 RPM on a standard day we are burning 7.7 GPH. The 172 has a capacity of 53 gallons. If we are indicating 100 knots ground speed on a GPS (1knot = 1 nautical mile per hour), we can calculate our rate as:

$$
Range = {53 \above 1pt 7.7} 100 = 688
$$

The result would be 688 nautical miles (this is burning every drop of usable fuel, not taking into account VFR or IFR reserves).