To avoid the coins to disapear from the islands, the coins had bigger values compared with a coins of the same size from Portugal.
In this case used coins "X Réis/1792" that, and since they had excess of "XRéis" coins at the Mint of Lisbon, and re-minted them as "20 reis".
They did the same for III Réis to "5 Réis" and "V Réis" do "10 Réis"
Enclosed is a coin from my collection where you can cleary see the old coin of "X Réis/1792".