The dan buoy is not engineered to be mounted upside down.
It should be mounted so that the deployment handle is up. Another way to say this is that the dan buoy needs to be mounted right side up. With handle up, it is easier to grab to readily throw the dan buoy, while also permitting water to easily drain through grommets in the bottom of the dan buoy outer sheath.
Mounting the dan buoy upside down can permit water to collect in the self-inflation mechanism, which can cause the dissolving pill to dissolve before you need it to. Mount the dan buoy right side up, with the handle upward. See the Dan Hold mounting bracket or the Dan Bag mounting bag.