RealVnc server does not show proper resolution after boot without monitor, Ubuntu 16.04

RealVnc server does not show proper resolution after boot without monitor.
vncserver -geometry 2560x1440   not working..!! Ubuntu 16.04 xserver is probably not compatible to
work with vncserver command. so there is one solution I came with,

solution:
add dummy display into /usr/share/X11/

use gtf command to generator proper resolution.
ex) gtf 2560 1440 60

/usr/share/X11/xorg.conf.d/xorg.conf/xorg.conf
====================================================
section "Device"
    Identifier  "Configured Video Device"
    Driver      "dummy"
    VideoRam 256000
#    VideoRam 2000000
EndSection

Section "Monitor"
    Identifier  "Configured Monitor"
    HorizSync 5.0 - 1000.0
    VertRefresh 5.0 - 200.0

# 2560x1440 @ 60.00 Hz (GTF) hsync: 89.40 kHz; pclk: 311.83 MHz
    Modeline "2560x1440_60.00"  311.83  2560 2744 3024 3488  1440 1441 1444 1490  -HSync +Vsync

EndSection

Section "Screen"
    Identifier  "Default Screen"
    Monitor     "Configured Monitor"
    Device      "Configured Video Device"
    DefaultDepth 24
    SubSection "Display"
    Depth 24
      Virtual 2560 1440
    EndSubSection
EndSection
====================================================

restart x display manager
sudo systemctl restart display-manager

check xserver log
sudo grep Modeline /var/log/Xorg.0.log


** Issue:
1. since it is placed in xorg.conf, it only work for dummy display for remote access,
 it won't work for physical monitor.  even rename it as 10-dummy.conf  it won't work with real monitor.