bluskis
I'm not an engineer so I'll take your word for it that sensors can't be fitted to operate at lower levels than quarter tanks but I'd prefer that to no warning at all.
It's odd that light aircraft seem to be the only form of engine-driven transport which don't have reasonably accurate fuel gauges and/or low fuel state warnings, yet the consequences of running out of fuel in the air are far more serious than on land or water.