Can't duplicate screens

I have an Asus desktop with a 1920x1080 monitor and a 1920x1080 TV monitor connected to a GTX560Ti graphic board with 385.41 driver. I can only extend them, I can't duplicate them. There is no Duplicate option.
The same thing happens on my Asus 1920x1080 laptop when I connect it to a projector. Very inconvenient.
If I connect the desktop or laptop to a lower res monitor, I can duplicate them, or extend them.
I have a 1600x900 and a 3200x 1800 laptop that will duplicate on a projector.
How do I make the 1920x1080 duplicate on the TV or projector?

Thanks Dude
The answer is that you can't duplicate if the ports do not come off the same GPU on some computers.
On the desktop, I had the TV connected to the iGPU port (because it was a VGA port) and the monitor connected to the eGPU DVI port. Connecting the TV to the other eGPU port (via adapter) solved the problem -- so I actually started thinking. -- The problem was that they were connected to 2 different GPUs. I was connecting the TV to the laptop via the HDMI port. That is apparently a different GPU since I connected it to the VGA port and it works like it should. The confusion was, I previously connected the laptop to a projector via the VGA and HDMI ports and had no luck. Guess I just need to try again. I believe I had my HP and my Dell connected to the projector via the display port and VGA port on the HP and the HDMI on the Dell (it has no VGA) and both duplicated. The HP is an i7 with external GPU also and the Dell is an i5. But at this point I am not sure of anything.
thanks again