Setting Window size of a Process using C# (Unity)

Question

I have a piece of code in Unity which opens another EXE file using the process.Start().

After the process starts, I am getting the main window handle and trying to set the position and window size.

This is my code:

Process process = new Process();
process.StartInfo.WindowStyle = ProcessWindowStyle.Normal;
process.StartInfo.FileName = "someApp.exe"
process.StartInfo.Arguments = "SomeArgs";
process.Start();

UpdateProcessWindow(process);

private void UpdateProcessWindow(Process process)
{
    // Waits for 10 seconds
    if (process.WaitForInputIdle(10 * 1000))
    {
        IntPtr hwnd = process.MainWindowHandle;
        SetForegroundWindow(hwnd);
        MoveWindow(hwnd, 500, 500, 1000, 500, true);
    }
}

Before this process is closed, if I manually modify the size of this window, then every time I start the process, the size is set to the manually edited size/position. I want to start the process with a 1000 width and 500 height always.

What am I missing here?