The basic spell attack table in RMSS Spell Law lists a modifier for "Full Cover" with the explanation "detected, but not sighted", which implies that detection is required. (RMFRP omits this explanation.) The RMSR does say basic spells are "directed at a target" (pg 99) which I take to mean you have to have some awareness of the target. I don't think this is explicit anywhere, but the basic spell attack table is presented with and explained with attacks, not with spellcasting, which again suggests it is like making an attack.
In our game, the GM has allowed the mentalist to use Presence for targeting, but he has had to make a spell mastery roll with Presence to get enough information to do so.
RMU moves the cover and range modifiers to the RR since there is no BAR, but otherwise it's basically the same.