Determine whether a card is being shown ({acard}?)

I would like to change parts of a watchface depending on whether a card is being shown on top of the face. For example, I would use the tag inside a formula for the Position Y to slide the time upwards to the top half of the display so it is visible while the card covers the lower part of the watchface. I would use something like:

Position Y: {acard} and -100 or 100

Would be great to have an {acard} tag... (or something to a similar effect...)