OK, thanks a lot, I'm beggining to understand the whole situation better.

So, to sum up :
If there's a vote before 15 minutes, a fraction of the rshares (linear between 0 and 15 minutes) won't go to the post (so increasing the payout value of all other posts - sames reward divided by less rshares), and the fraction of curation rewards of this "ghost" vote value (generated by all future votes) will also not be attributed to anyone (once again increasing value of all other posts).

Have I finally understood the thing or not ? :D