Sorry this dropped off without me realising you’d posted.
Take all the air out of your septune and see how much space there is between the rocker arm and the seatpost pillar.
You *might* have 3mm, but I believe the majority of frames have less than this, due to the eye to eye length being the same, the difference between 47mm and 50mm means that the rocker arm travels further up towards the frame (probably around 6mm further at the end due to leverage).
200×50 fits because it pushes the shaft further away from the frame enough for it not to be an issue. You also get around 7mm more travel and a slightly steeper head angle.