Oh boy I just found it one minute after post hahahahaha I will keep the post in case someone need it on the future, the text im talking about its in page 477 (Cover > Special Special Circumstances)
"Your GM might let you reduce or negate cover by leaning around a corner to shoot or the like. This usually takes an action to set up, and the GM might measure cover from an edge or corner of your space instead of your center."
####################################
Some months ago reading the Core I found a text saying something like "you GM may let you attack an enemy after hide, maybe leaning out of the wall and shooting but maybe it cost an action"
(Something like this i dont remember, if I do i could find it with ctrl+f xD) and well i need to check it for situations where a player hide enemy and then attack with bow but want keep the enemy flat-flooted
Any idea of where is this text?