Uncertainty regarding the knee wall as a building regulation in the development plan

Is it even reasonably possible to build a single-family house with 1.5 stories in WA4 (ridge height max. 9m)

We have a 10-meter wide! house and end up with a knee wall of 125, but a roof pitch of about 26, something around 7.xy. You can sketch it yourself on graph paper: one box up and two to the right/left is 30 degrees. Or you use a protractor… the wider the house, the higher the central eave rises.