Method for how much cinnamon to add to recipe
There aren't really any hard and fast rules when it comes to deciding how much cinnamon to start with.  There are certainly considerations when thinking about how much flour, milk, fat etc. to use in recipes and this is thrust of the book to which you refer. Baking is essentially chemistry and you need to get the proportions of the chemicals right to produce fluffy pancakes and light sponge cakes etc.  When it comes to flavouring the results of that chemistry there is less restriction but balancing the flavours should be a consideration. 

One thing to think about is 'what do I want to end up with'? For example, are you aiming for apple pancakes, apple and cinnamon pancakes or cinnamon and apple pancakes.  If you only want a background cinnamon flavour to an apple pancake, then start with a smaller quantity of cinnamon.  If you'd like something that's more balanced in apple and cinnamon flavours then add more cinnamon to the same quantity of apples you used before.  If you're after something that's essentially cinnamon in flavour but with some apples there to add body then have at it with the cinnamon and go easy on the Bramleys'.

I've done some reading in the copies of Larousse Gastronomique and McGee on Food and Cooking we have at home and also consulted a book called The Flavour Thesaurus. None of these suggest any ratios of cinnamon to other ingredients. The addition of flavouring will always be subject to both personal taste and the needs of the recipe.  The proportions of the 'building blocks' of a recipe, particularly baking, can be much more easily defined and, to a degree, calculated.  Consider this, if you left the cinnamon out of your apple pancakes completely, they'd still be pancakes and have flavour. If you omitted the flour you'd have an mess.

As an addition, in series 2 episode 3 of Jamie Oliver's 30 Minute Meals, he raves about sprinkling cinnamon over Sicilian fish dishes. This is an example of there being no set rules about how much of a flavouring to use or where to use it.

I'll try and add some inline references to this tomorrow.