How much sugar are you adding?
You know what batter consistency you want for waffles, right? Just mix the ingredients you have, see the batter consistency then add whatever sugar you are throwing into the mix and then add enough water to get the same batter consistency.
better yet, sprinkle the sugar on the cooked waffles instead of adding to the mix. ;-)
Egg size isn’t critical... if you are doubling the mix, use two eggs.
Why would a recipe call for 'extra' large egg if the egg size is not critical? Wellll 'critical' is your word.