I replaced the glass on my T6 this week. If it's the same / similar to yours, which it sounds like it might be then I have the following experience:
- The top screw to attach the strut to the glass is slotted for a flat head screwdriver. This screw should tighten and leave a small amount of play so that the strut can rotate on the screw.
- The bottom screw uses an allen key and tightens into the nut.
- The nylon washers for these two screws are different thicknesses. Check the fridge side (If it is still assembled to check the washers, but from memory, the thin one goes on the top.
There is no way to alter the strength of the gas strut to aid in a soft close. The strut makes a nice strong triangle between the glass and sink top when it is open, but when you close it, this collapses to a not so strong straight line. The only way would be to add a soft close catch somehow vertically from the surface to 'catch' the glass as it falls.