Traditionally, there are three steps from the nave up to the
solea, with the iconostasis separating the
solea from the altar, the altar being at the same height as the
solea. The OED listing is in the pic. Oddly, the
Wikipedia entry uses
soleas even though it begins by saying the Greek form is σολέα [solea] and lists σολέας [soleas] as 'other form' — and, in the final paragraph, uses
soleas the first time but then uses
solea the remaining four times.
I've never encountered
soleas in normal usage. A Google search for 'orthodox solea' returns 'about 361,000 results' whereas 'orthodox soleas' only returns 'about 91,300 results'.