It depends what you mean by "a few mouthfuls of dry". They don't need much dry food as it's very calorific, so I'd guess they are getting enough. If they're not losing weight, they must be. When I fed dry food with just a bit of wet, I gave about 30g dry per day plus one pouch of wet food. That was for youngish, reasonably active (and good sized) cats. If you measure out 30g of the RC, you'll find it doesn't look much.