You can use up to 30% if the grainbill without worrying about the supposed "cidery" taste...
We need to stop this repeating this oversimplification.
That's actually another one of those brewer's myths that new brewer's tend to repeat over and over like canon, without full understanding what they're talking about.
Too much sugar, in a recipe can give off off flavors, or make a beer cidery, but we're talking about someone who wants to bump up the alcohol on his 6 pounds of extract beer by adding another 6 pounds of table sugar to it.
That whole thing about not adding sugar or else you make "cidery" beer is one of those little "chestnuts" that noobs repeat without thinking deeper about it. When we talk about it being a bad thing, is when the ration of sugar to malt quite high, like frat boys trying to bump up their coopers can...yeah that's a bad thing...but we're not talking about that here, we're talking about an acceptable brewing process for many styles of beer...
I mean do you like Belgian beers? Are they crappy tasting because of the simple sugars that are added? If you like them, that's how they achieved the beer you like.
Belgian beers are a style that are supposed to have simple sugars in it. It raises the abv, but it also cuts down on some of the body, promotes the formation of certain flavors and helps dry the beer out.
A pound or two isn't going to affect the beer in a negative way, especially if the recipe calls for. Even a cooper's which people want to deride, or some others suggest replacing with malt extract, is really meant to have exactly the amount of sugar the recipe might call for. But if you willy nilly add a couple more pounds to it, that's another story.
It's about balance in a recipe, the correct amount of sugar in a recipe is fine, and often serves an important purpose.
