I have never seen an adult of this species so I have nothing to go by. I read somewhere that an adult is around 25mm, that would put it just under an inch. Are they considered thumbnails? The care sheet section here shows a video with 6 of these in a 18x18x24 so that leads me to believe they can't be that big.

Is there another frog that you could mention that is the same adult size as E. anthonyi Santa Isabel?