If I were writing this example by hand I would just put these two crotchets here with a 2 tuplet number on top, but in Dorico I’m only able to type it as a 4:5. I think I might be thinking of the ratios wrong…
The reason you can’t simply display it as “2” is because the resulting ratio (“2 in the space of X”) is not an integer. Y:X is typically displayed as integers.