Enable snap layout on custom maximize-restore button and apply shadow around borderless form

Question

I have a borderless form with a custom max-restore button, the max-restore button is a custom class with overriden WndProc that returns HTCAPTION when the message is NCHITTEST, that properly shows the snap layout when mouse is over. enter image description here

However, if in the constructor of the form I put the DwmExtendFrameIntoClientArea method, there is a nice shadow around the form but the snap layout does not appear anymore. enter image description here

How can achieve to have both.

This is the form code:

    public partial class Form4 : Form
    {
        private MaxButton maxButton;
        public Form4()
        {
            InitializeComponent();
            maxButton = new MaxButton();
            maxButton.Location = new Point(50, 50);
            maxButton.Size = new Size(50, 50);
            Controls.Add(maxButton);

            // Set the border thickness
            MARGINS margins = new MARGINS
            {
                Left = 1,
                Top = 1,
                Right = 1,
                Bottom = 1
            };

            // Apply Border
            DwmExtendFrameIntoClientArea(Handle, ref margins);
        }

        protected override void WndProc(ref Message m)
        {
            if (m.Msg == 0x0084)/*NCHITTEST*/
            {
                Point screenPoint = new Point();
                GetCursorPos(ref screenPoint);
                Point clientPoint = PointToClient(screenPoint);

                if (clientPoint.Y <= 10)
                {
                    if (clientPoint.X <= 10)
                        m.Result = (IntPtr)13/*HTTOPLEFT*/ ;
                    else if (clientPoint.X < (Size.Width - 10))
                        m.Result = (IntPtr)12/*HTTOP*/ ;
                    else
                        m.Result = (IntPtr)14/*HTTOPRIGHT*/ ;
                }

                else if (clientPoint.Y <= (Size.Height - 10))
                {
                    if (clientPoint.X <= 10)
                        m.Result = (IntPtr)10/*HTLEFT*/ ;
                    else if (clientPoint.X < (Size.Width - 10))
                        m.Result = (IntPtr)2/*HTCAPTION*/ ;
                    else
                        m.Result = (IntPtr)11/*HTRIGHT*/ ;
                }
                else
                {
                    if (clientPoint.X <= 10)
                        m.Result = (IntPtr)16/*HTBOTTOMLEFT*/ ;
                    else if (clientPoint.X < (Size.Width - 10))
                        m.Result = (IntPtr)15/*HTBOTTOM*/ ;
                    else
                        m.Result = (IntPtr)17/*HTBOTTOMRIGHT*/ ;
                }
                return;
            }
            else if (m.Msg == 0x0083)/*NCCALCSIZE*/
            {
                return;
            }

            base.WndProc(ref m);
        }

        public struct MARGINS
        {
            public int Left;
            public int Right;
            public int Top;
            public int Bottom;
        }

        [DllImport("user32.dll")]
        static extern bool GetCursorPos(ref Point point);

        [DllImport("dwmapi.dll")]
        public static extern int DwmExtendFrameIntoClientArea(IntPtr hWnd, ref MARGINS pMarInset);

And this is the custom max-restore button:

public class MaxButton : Button
{
    protected override void WndProc(ref Message m)
    {
        if (m.Msg == 0x0084)
        {

            Point screenPoint = new Point();
            GetCursorPos(ref screenPoint);
            m.Result = (IntPtr)9;
         
            return;
        }
        else if (m.Msg == 0x00a1)
        {
            Form form = FindForm();
            if (form.WindowState == FormWindowState.Maximized)
            {
                form.WindowState = FormWindowState.Normal;
            }
            else
            {
                form.WindowState = FormWindowState.Maximized;
            }
            return;
        }
        base.WndProc(ref m);
    }
    [DllImport("user32.dll")]
    static extern bool GetCursorPos(ref Point point);

   
}

I have tried put the DwmExtendFrameIntoClientAreaMethod in other parts for example when handling the NCPAINT message, but results are the same