pass through, go smoothly
亨 centers on unimpeded movement or progress: things passing through without obstruction and going smoothly.
亨 is thought to depict a container or vessel with a lid, suggesting something passing through or being offered smoothly. The exact historical development is uncertain.
The top 亠 is like a lid, and the bottom 口 and 了 form a container with an opening. Picture something sliding through the container effortlessly: it passes through and goes smoothly.
For コウ, imagine a smooth-flowing current (コウ) passing through the container: current -> コウ, and everything moves without obstruction.