How do you decide when to deviate from baking ratios?
As you asked more than one question here, I'm going to focus on the title: &quot;How do you decide when to deviate from baking ratios?&quot;.
And the answer is: when you want a different result.
Ratios are useful guidelines when coming up with new recipes.  They're not laws that need to be followed exactly.  If you think something came out a little dry, then you make a note to add a little more liquid or fat the next time around.