how to apply context docBase for network drive?

IDE version 15.

i did setting  network drive : \\192.168.0.XX\common_file to  x:\

(windows 10)

common_file folder have a, b sub folder and a.jpg, b.jpg.

common_file --a -- a.jpg

                     --b -- b.jpg

in IDE,  i did tried setting Run > edit configurations > Deployment tab

external directory path :     x:\a , application context : /common/a

 mywebsite/common/a/a.jpg  => work!!

but, external directory path :     x:\ , application context : /common

 mywebsite/common/a/a.jpg  => not work!!

i want to setting  x:\ , application context : /common

where is problem???