Gas drops don't make any difference with the size of a rabbits fecal droppings. Indigestible fiber does. Gas drops are for a rabbit with an upset stomach from gas build up that usually will cause a lack of appetite. It's the lack of appetite that will cause smaller poop or no poop.
But your rabbit isn't showing any of these signs of an upset stomach or decreased appetite, correct? So the smaller poop that your rabbit is having is either going to be from not eating as much hay as usual or from ingesting too much fur while grooming. If your rabbit isn't molting a lot right now, then you need to look at your rabbits hay consumption, if it's decreased, and if it has, why. Did you happen to just start a new batch of hay that maybe your rabbit doesn't like as much?
To increase hay consumption you can try reducing pellet amounts. But you need to keep a really close eye on the hay eating, because if your rabbit doesn't start eating more hay with reduced pellets that same day, then this isn't a good thing and could indicate there is a health issue going on.
