That is not a tension bolt. It is a shoulder bolt that is the pivot for the trip function.
The trip tension is the metal part of the mount and the indentations on the sides are what holds the plastic part in the mount and what allows the trip function to work.
Some slack is NORMAL.
If you insist on messing with the tension, you can open the mount, squeeze the sides of the metal to reduce movement and then close it. The transducer will have to be whacked harder to release.
Humminbird Helix 12 SI, 1198c SI, 1198c SI, ONIX 10 SI NT, 360, RC-1