Yes, it really does stick out so far in the back... I don't know what the developer was thinking.
Have a look at
https://www.displayspecifications.com and search for the C27HG70. The dimensions including the stand say 390.7mm and I would say that is correct. I recommend a work surface with a depth of at least 80 cm, then you'll have enough space in front of the monitor for the keyboard and other things.
If necessary, you could also mount the monitor on another stand using the included adapter. Details in the operating instructions.
Otherwise, the monitor is quite ok. The 144Hz make the picture much smoother than with the usual 60Hz. I used it with a GTX1080TI, i.e. without Freesync... works well, either with Vsync or without it, depending on what's going on.
