Thrones can be distinguished from sleeping platforms because thrones tend to be centered on one wall and positioned so that they face a doorway. Thrones are wider than they are deep. They usually have sub-spring beams positioned on either side where fabrics could be hung. Thrones tend to have contact with one or possibly three walls, but never with only two.
(Peter Harrison, The Central Acropolis, Tikal, Guatemala: A Preliminary Study of the Functions of its Structural Components during the Late Classic Period, 1970. Unpublished PhD dissertation, University of Pennsylvania, p. 179)
The bottom scene comes from a painted ceramic found in Burial 196 at Tikal. Notice the tied-back curtain above and to the side of the throne. Also note the jaguar pelt slipcovers on the throne, which in addition to being associated with royalty, doubtless made this style of furnishing more inviting to sit upon.