Resize Borderless WinForm with sub controls on border

Question

is there a way I can resize a borderless form with controls that are on the border with one code?

The Problem is I can't resize when I put a close, maximize and minimize button in the top right corner.

Close, Maximize & Minimize Buttons Image

I know, it's possible with this code to resize all sub controls. But the problem is I can't use the full space of the Buttons. If I m too near to the border with my cursor it switches to the resizer.

private void Controls_Bar_Top_Load(object sender, EventArgs e)
    {
        subClassChildren(this.Controls);
    }
    const int edge = -32;

    class MouseFilter : NativeWindow
    {
        private Form form;
        public MouseFilter(Form form, Control child)
        {
            this.form = form;
            this.AssignHandle(child.Handle);
        }
        protected override void WndProc(ref Message m)
        {
            const int wmNcHitTest = 0x84;
            const int htTransparent = -1;

            if (m.Msg == wmNcHitTest)
            {
                var pos = new Point(m.LParam.ToInt32());
                if (pos.X < this.form.Left + edge ||
                    pos.Y < this.form.Top + edge ||
                    pos.X > this.form.Right - edge ||
                    pos.Y > this.form.Bottom - edge)
                {
                    m.Result = new IntPtr(htTransparent);
                    return;
                }
            }
            base.WndProc(ref m);
        }
    }
    private void subClassChildren(Control.ControlCollection ctls)
    {
        foreach (Control ctl in ctls)
        {
            var rc = this.RectangleToClient(this.RectangleToScreen(ctl.DisplayRectangle));
            if (rc.Left < edge || rc.Right > this.ClientSize.Width - edge ||
                rc.Top < edge || rc.Bottom > this.ClientSize.Height - edge)
            {
                new MouseFilter(this.ParentForm, ctl);
            }
            subClassChildren(ctl.Controls);
        }
    }

I just want a code where the resize pointer just shows up when I hit the shadow of the control. Right now it shows already up when I am like 5px away from the shadow.

The Code I use for my form to resize is this:

 protected override void WndProc(ref Message m)
    {
        const int RESIZE_HANDLE_SIZE = 10;
        switch (m.Msg)
        {
            case 0x0084/*NCHITTEST*/ :
                base.WndProc(ref m);

                if ((int)m.Result == 0x01/*HTCLIENT*/)
                {
                    Point screenPoint = new Point(m.LParam.ToInt32());
                    Point clientPoint = this.PointToClient(screenPoint);
                    if (clientPoint.Y <= RESIZE_HANDLE_SIZE)
                    {
                        if (clientPoint.X <= RESIZE_HANDLE_SIZE)
                            m.Result = (IntPtr)13/*HTTOPLEFT*/ ;
                        else if (clientPoint.X < (Size.Width - RESIZE_HANDLE_SIZE))
                            m.Result = (IntPtr)12/*HTTOP*/ ;
                        else
                            m.Result = (IntPtr)14/*HTTOPRIGHT*/ ;
                    }
                    else if (clientPoint.Y <= (Size.Height - RESIZE_HANDLE_SIZE))
                    {
                        if (clientPoint.X <= RESIZE_HANDLE_SIZE)
                            m.Result = (IntPtr)10/*HTLEFT*/ ;
                        else if (clientPoint.X < (Size.Width - RESIZE_HANDLE_SIZE))
                            m.Result = (IntPtr)1/*HTCAPTION*/ ;
                        else
                            m.Result = (IntPtr)11/*HTRIGHT*/ ;
                    }
                    else
                    {
                        if (clientPoint.X <= RESIZE_HANDLE_SIZE)
                            m.Result = (IntPtr)16/*HTBOTTOMLEFT*/ ;
                        else if (clientPoint.X < (Size.Width - RESIZE_HANDLE_SIZE))
                            m.Result = (IntPtr)15/*HTBOTTOM*/ ;
                        else
                            m.Result = (IntPtr)17/*HTBOTTOMRIGHT*/ ;
                    }
                }
                return;

            case WM_NCPAINT:
                if (m_aeroEnabled)
                {
                    var v = 2;
                    DwmSetWindowAttribute(this.Handle, 2, ref v, 4);
                    MARGINS margins = new MARGINS()
                    {
                        bottomHeight = 1,
                        leftWidth = 0,
                        rightWidth = 0,
                        topHeight = 0
                    }; DwmExtendFrameIntoClientArea(this.Handle, ref margins);
                }
                break;
            default: break;

        }

        base.WndProc(ref m);