Sorry, John, they don't roll about halfway, but occupy anarchically the space in the box.
Heri needed the window to be open, but these windows are automatically locked, once pushed completely. Nice but vain demonstration.
Then Heri needed someone to maintain the shutters up, because if they're not enrolled they fall if you don't secure them firmly.
The shutters can be raised from the outside, I have done it many times at my own home. I agree the distance individual shutters can be raised depends on several factors. However, it is irrelevant whether the window is locked or unlocked as the window has no relevance to the shutter.
As you pointed out, for anyone to be able to pull up the shutter far enough to climb in they need access to the strap inside thus an open window is a necessity.
The photos taken of the childrens bedroom window show the strap on the rhs (looking from inside). That is the same side the sliding pane opens from. Thus any prospective intruder only needs to lift the shutter about 300mm, slide the window across (if unlocked) and pull the strap sufficiently to engage the mechanism and lock the shutter in position. All they have to do now is continue to pull the strap until the shutter is sufficiently raised to afford access.
