Some very interesting posts, like this one, which has links to some more extensive discussions and websites that I consulted, too, describe some aspects of the method used to prepare and bake the batter, affecting the end result.  However, a sentence in one post:     You can play with the ratio of ingredients every which way and still end up with a batter that rises tall.   left me quite baffled, because I thought: surely the composition of the batter must matter to some extent...  From a little research on the topic, I found that, indeed, the proportions of the ingredients vary widely between different recipes, but I could not find any extensive account of how that impacts the outcome.  See below the links to each recipe I looked at, and the % of ingredients, in order of egg to flour ratio.  Allegra McEvedy Egg = 19%, Flour = 24%, Milk = 57%, Water = 0%, Egg/Flour = 0.80  Tom Kerridge Egg = 26%, Flour = 29%, Milk = 45%, Water = 0%, Egg/Flour = 0.89  BBC food Egg = 22%, Flour = 22%, Milk = 44%, Water = 11%, Egg/Flour = 1.00  Serious Eats Egg = 36%, Flour = 27%, Milk = 32%, Water = 5%, Egg/Flour = 1.33  Mary Berry Egg = 31%, Flour = 21%, Milk = 47%, Water = 0%, Egg/Flour = 1.50  James Martin Egg = 33%, Flour = 18%, Milk = 49%, Water = 0%, Egg/Flour = 1.78  However you look at it, Egg/Flour ratio, (Egg+Flour)/(Milk+Water) ratio, there is a huge variability.  I experimented a bit, although I did not make all of them. Allegra McEvedy's version is my favourite so far, whereas other recipes (I won't say which ones) gave me stodgy, undercooked puddings, a completely different thing, despite the fact that the method was to all practical purposes the same.    Q As per title of this post, would anyone be able to please point me to posts or websites describing how the batter composition affects the end result, e.g. in terms of shape, texture and taste? 
There’s a food processing trick, where producers use dextrin to keep the coating crisp for hours. You simply replace some of the flour (around 20%) in your recipe with dextrin and you’re good to go.  As the other answer mentions, multiple layers also helps creating a thick barrier to slow down moisture seeping into the coating. You can use dextrin in both layers.  Once you’ve adapted your recipe to use dextrin, frying followed by rapid cooling should give you a good result. 