Hi lux welcome to the Decorating Forum - great to meet you

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I actually once tested how far the water will spray when washing your hair in order to work out how long a piece of glass you need to create a walk-in shower. According to my scientific testing

it will spray 1350mm. So I always make sure the fixed glass for a walk-in shower is 1350 long.
With your fixed glass being 1200mm it is touch and go. If you don't put a glass door then you may get a little water spray outside the opening of the shower but not much. My main concern is you have only allowed 500mm for the opening. I would allow 750mm instead. That is the size of an average shower door and a comfortable opening to walk through. So then your fixed glass would only be 950mm. With that size fixed glass I would put a glass door on.
Have you a plan of the whole bathroom?