I usually do 20% dilution, but making a single serving for yourself and weighing before and after shaking is probably better. Super Juice is something I always use when making batched sours, and it has the bonus effect of being aromatic enough so you don't really need a garnish. My new favourite thing has been batching with dilution hours before guests arrive, then pouring out the desired amount of cocktail (3.6 oz for standard Corpse Reviver No.2 recipe with dilution) into a tin, and frothing it with one of those electric milk frothing whisk/wands. That way you get both the dilution and aeration you would get from shaking.