The frame
Frame listings print a size name and a height, and only the size name has a partner. A Queen frame is sold to carry a Queen mattress, so the word on both listings has to be the same word. Twin and Twin XL are different words, and this catalog files zero Twin XL frames.
The height is the frame’s own figure. Nine of the ten frames that state a height give the same 14 in. Nothing stacked above has to agree with it, and it stays out of the pocket arithmetic, because the quilted cover is fitted to the mattress rather than to the frame.
What a frame listing leaves out is the gap underneath. Seven listings mention storage under the bed, in words that run from storage space to large under-bed storage, and zero of them give that space a height. The frame height is not that number, and this site does not use it as one.
Capacity figures appear on two listings and are printed as the listings state them. Nothing on this site confirms what any frame will carry. Setup and use belong to the maker’s instructions.