Hi Dadanawa
I'm not quite sure whether you are asking a question or making a statement but whatever, it seems to be some unnecessary arithmetic done to calculate a number that is not really needed.
If you don't fly CDFA approaches, you level off at the MDA of 980ft and if you do not have the required visual references by the missed approach point at D1.9 ISAB then you go around. If you do have the required visual references and it is safe to do so, you land.
If you do fly CDFA approaches, you add a figure that your operator calculates for your aircraft (lets assume 50ft), to the MDA of 980ft to produce a 'derived DA' of 1030ft. If you do not have the required visual references at the derived DA, you go around. If you do have the required visual references and it is safe to do so, you land.
Presumable there may be some ISA temperature corrections to consider but in the UK that doesn't concern me too often and being an escapee from Rotorheads I only have to think at 100kts
Cheers
TeeS