See Card Quantity for full details on how Zoop calculates card quantities.
If you want Zoop to create multiple copies of a card when exporting you can take advantage of the encounter set number field in SE. Here’s an example
In this example the encounter set number on the card will look like this
Zoop will create two copies of the card. This will only work if you use the format <number><hyphen><number>
. Any other content will result in a single copy of the card. You do not have to specify the second number (which indicates the total number of cards in in the encounter set) for this to work.