I wouldn't say that FG 1.028 , down from 1.098, is exactly low, but I've faced this too and solved it by back adding lactose. I'd suggest making little mini-samplers and carbonating with a carbonator cap. Then start with the equivalent of 8oz lactose, or alternatively 4 oz of each. Adjust to taste.
I found that doing this with lactose adds an artificial-sweetener taste that will diminish after a couple months.