No transatlantic slur intended ;-), but I we often hear advice along the lines of 'if you select your site right and scrape a trench, you will not have a problem', which might be OK in many areas of North America, but is not always practical in the very mixed conditions that we get in Europe.
In many areas, our backpacking is through high mountain country with little shelter and rocky ground interspersed (certainly in the UK!) with sodden moss - your chances of arrnging an artificial crown are zero.
I have often recalled Ray Jardine's advice to find a bed of dry 'duff' with a wry smile, as the water sluices under the bathtub groundsheet!
I have not been to the Pyrenees myself, but I have read plenty of accounts and seen lots of photos. Given the outcropping terrain and the possibility of flash flooding, I would advise that you take some system (tent inner, bivy or improvised bathtub groundsheet) that will withstand a certain amount of water running right under your carefully pitched shelter!