The hood presently fits with a bit of a point at the top of the crown. You need to remove this point smooth it out .
-At the crown of the head 3.0 cm needs to be added in width(depth) per side (total with both sides increases to 6.0 cm.)
-This opening extends 4.0cm beyond the crown and would blend to zero.(towards the front of hood)
-This opening would extend 10.0 cm (at the back of hood/nape of neck) and blend to zero.
-Because you are adding more depth(width ) to the hood it would increase the measurement for hood CB length. 51.0 cm is an approximate measurement.