I'm guessing you purchased an Anova?
If so, the container is a bit large. Anova recommends a tank size of 4-5 gallons for their Precision cooker, and 5-6 gallons for the Anova One.
Although I'm no expert, I would guess that you might have uneven water temperatures if the vessel is too large, with the machine struggling to get it to, and to keep it up to temperature. If you decide to go with the 6.25 gallon cooler, I would not put the opening in the corner, because I would guess the opposite side of the cooler might not be up to specs temperature-wise