Question about Safety 1st Extension for door protection grille

These 14cm are fixed. You can take the min. length and the max. length without extension from the normal door grille. This is the possible width. The width of the stairway must be within this range plus the additional extensions.
The 91cm minus the 14cm extension = 77cm and is therefore within the 73-80cm.

I would say 94 cm is the minimum width. We have about 100 cm here. 91 cm is probably not possible.