The 亠 cap on top is the indexing Kangxi radical for 亨. Originally 亨 depicted an ancestral altar or temple with offering inside; the roof-line of the temple survives as the 亠 cap that anchors the graph for traditional dictionary lookup.
The 口 in the middle represents the chamber of the ancestral altar where offerings were placed. It pictures the enclosed sacred space, contributing to 亨's meaning of smooth ritual flow that extends to 'prosperous, going well' in 亨通.
The 了-shaped bottom is a stylization of the altar's pedestal or supporting base. It grounds the altar-chamber-roof stack and completes the temple silhouette; semantically it reinforces the sense of ritual completion that underlies 亨's 'going through smoothly' meaning.
