I am planning to install laminate flooring in a room the main level of a concrete slab. After peeling off the original carpet, there appears to be a few inches of uneven concrete that runs along the drywall covering the exterior walls (but not the interior walls). (Please see attached photograph.) There is around an inch or two of blue polystyrene with a plastic moisture barrier between the "outer" concrete and "inner" concrete. The "inner" concrete appears to have been levelled (1/8-inch maximum imperfections), but approximately 1/2 inch lower than the "outer" concrete. What should I do to raise the "inner" concrete floor to achieve a constant level throughout the room? Would I need to use levelling compound on the few inches of "outer" concrete? Unrelated to the topic of flooring: Is the protruding "outer" concrete part of the concrete slab foundation? Thank you in advance!