Blendshapes different in Blender then in Unity

I have a generic 3d head with blendshapes on it. I have added an extra blendshape called “BaseShapeHead”. I sculpted the head to make it more oval. Didnt change anything regarding vertex count. Now if I blend between 0 and 1 it looks perfect.

I import the model in Unity but the change is minimal. I change the slider from 0 to 100.
Now if I change it to 300 then I see the change in shape of the head but the whole face is then screwed. What is the reason for this? And can I fix this?

I will post some screenshots tomorrow.