I think one of the most common things people do that gives them the 'impression' an ICE has less available power .. than it really does .. is they stay at very low RPMs in high gear.Yeah I have been trying (and did some today actually) to use lower gears for LB, but holding it in LB in 3rd at 50mph sounds crazy, I will make sure to try that out tomorrow and see what happens.
Once warmed up and such .. you can keep LB up to about ~2,900 RPMs 3rd , 4th, or 5th gears .. it just mean different MPH speeds to reach that ~2,900 RPMs in those different gears.
Also keep in mind the Gen1 Insight has some tall gears .. forgetting about LB for a moment .. you could go 100 MPH in 3rd gear and not yet reach the ICE RPM red line ~6,000 RPMs.
Higher gears to give lower RPMs and less power at a given speed .. those are for when you need/want less ICE output power .. and thus consume less .. thus get higher MPG at the same speed and power.
When you need/want more power .. acceleration .. hill climbing .. etc .. you need higher ICE RPMs at that same ICE Load to get higher ICE output power.
The Gen1's max non-LB ICE power ~50kw is not available at slower than 5,700 RPMs .. LB's max about ~20 kw is not available slower than about ~2,900 RPMs .. of course if you need/want less than that max .. stay in a higher gear at lower RPMs and enjoy the higher MPG.
If you ever have to choose between LB in lower gear .. or non-LB in higher gear .. it's more energy efficient to be in LB than to be in higher gear non-LB .. of course .. if your power needs are low enough and you can have both LB and higher gear that would be best .. but if you have to choose between them .. choose the gear that gives you the power you need/want in LB.
The one thing to keep in the back of your mind when it comes to lower gears and higher RPMs .. many people find more power to be addictive .. if you develop a 'lead foot' that psychological effect will reduce your MPG .. although a LB lead foot is still more efficient than a non-LB lead foot.