Fitting lockable roof handles

Hello all,
I purchased a lockable roof handle for my golf mk 1 rivage cabriolet. Firstly I realised that the one I broke was the lockable one but the one on the drivers side was not a lockable one. Anyway i have since sourced another lockable one but am now having problems fitting it. I am attaching it by putting the roof down and then screwing the two black screws on that face upwards and then finally screwing the inside larger screw. But i am finding that the lockable roof handle is not locking so i cannot close it tightly/at-all. Is there a special technique to fit the lockable handle?

Finally does it matter if one of my handles is lockable and one is normal? the reason I broke the lockable one was because i tried to tighten them as had lots of judering when going over bumps etc.
i presumed that by decreasing the movement in the silver hook that it would kep things tighter. Obviously I did it too tight and snapped the handle. Should I keep them both the same or is it ok to have one lockable and one not?

Any thoughts/tips/idea's what is going on?

All help is appreciated.

Thanks guys!

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