Vincent, As far as I know, the use of preposition is pretty flexible and sometimes, they depend on the flow of your writing and what you prefer to express. I guess maybe that's a reason Clive suggests you write a short paragraph.
The key to learning prepositions, I think, is to understand their meaning in different contexts and not memorize what others tell you in one context and apply it to every context. Using the wrong preposition can be disasterous. For example, may not be a good example,
There's a spoon on your head
There's a spoon in your head.
They are both correct but if you do not provide a context, I would suggest you use 'on' but in some contexts, 'in' is the correct choice. I hope you understand me.