Keep in mind that mixing the levels of hot and cold water isn’t the only factor in the final temperature. It’s also the actual temperature of the water in the pipes. Depending on where your pipes run, the cold water in the pipes may be warmer or cooler than the underground source of the water. The hot water may also have cooled more or less since leaving your hot water heater. Initial temperature may therefore be too hot or cold compared to where it ends after a period of use.