Right side 殳 - a hand wielding a long-handled weapon, the indexing radical. Suggests guards posted at the great hall; combined with the roofed ritual scene on the left, the whole character pictures the throne room secured by armed retainers.
Top-left 尸 - originally a seated figure, here standing in for a roofed structure (the same architectural sense seen in 居, 屋, 屏). Anchors 殿 in the family of dwellings and large buildings.
Lower-left 共 - two hands raising an offering. Inside the roof it pictures formal ritual being conducted indoors, the ceremonial weight that pushed 殿 toward 'grand hall / palace audience chamber' rather than ordinary house.
