In your opinion, how much space between the tip of your toes and the tip of the shoe is too much? How much is too little?
I guess half inch is about right, but sometimes you gotta have a little more than that bc the 1/2 size down is too small (or maybe that shoe model just isn't right for you). One could maybe get away with a little less, but again, that is a little less than a 1/2 inch when you are
standing up straight with your weight centered and someone else is checking it and its the evening (when your feet have expanded to their largest size).
Checking the size of a shoe sitting down is useless and misleading.
Also keep in mind that the big toe isn't the longest toe for some people. I have a morton's toe, so my second toe is longer than the big toe. Honestly though its hard to use my second toe for measure so typically I still measure with the big toe but I keep in mind that the second is a little longer. Every shoe has a different shaped toe area. Some are more square, others are pointy. Some are sharply slanted to toward the big toe and these shoes I cannot wear at all due to having a morton's toe. I look for more square shaped toe boxes.