That shallow angle can be found optionally in window sills too. You can sand off a part of the sill to add a positive drainage angle. You counteract the slope b

That shallow angle can be found optionally in window sills too. You can sand off a part of the sill to add a positive drainage angle. You counteract the slope by using sill wedges to keep your window level. There also exists more proprietary molded plastic products that do it all in one.