[Is it Friday Yet]

I have a 21 CRF1100A (Base, Stock Tires, until yesterday) 4.9 gal tank. I photograph every fill up.
Here is the generalization.
3.3 gal consumed - single gray bar
3.5-3.6 gal consumed - solid red bar (anecdotal)
3.8 gal consumed - blinking red bar - starts (anecdotal) I have had as much as 52 miles computed range at fill up when down to a blinking red bar. It may have started a few to as much as 5 miles earlier.

I always fill the tank to the bottom of the nozzle stop and fill the last 1/2 gal inspecting visually.
Here is my milage log (I know, OCD Much?). This is status at the pump.

Still working on Oct 9 fill. Prepping AT for a camping trip. Installed 50/50 tires, heated grips ,12v adapter, center stand and had surgery on my ear a few weeks ago... haven't been able to put on a helmet It's almost healed though.