Refusing to use the bottom 20% of your 300 mile pack is astonishing to me.
I understand having some buffer in case you need to divert to an alternate charging location but most people in most parts of the US don't live or travel places where charging stations are THAT far apart.
And there is no danger to battery health with driving down to 5% or lower state of charge. You're SUPPOSED to go that low on long trips. The only potential impact to battery health is if you leave it parked at a super low or super high state of charge, and even then doing so for a day or two on rare occasions is not gonna be a problem. Furthermore most EVs already lock off a small portion of the pack's range specifically for battery longetivity so unless you're in a Tesla or are under a recall or something you shouldn't worry about this so much that you refuse to use the last twenty percent
Use your whole battery! It's there for you to