Please be aware that a Cap device (intended for Ceiling mount, but that can also mounted on a wall) has a shape of the emissions that can be imagined as a spherical cap (when mounted on a ceiling omnidirectional in the horizontal plane and downwards only in the vertical plane, see:
http://forum.mikrotik.com/t/cap-ax-gen-6-mediocre-performance/176254/1
A Wap device (intended for Wall mount) is instead a more directional device projecting most of the emissions in a 60 to 90°, maybe 120° wide sector, see:
http://forum.mikrotik.com/t/wap-ax-as-replacement-for-old-unifi-ac-pro/180280/1
http://forum.mikrotik.com/t/wap-coverage-picture-included/179859/1
In other words, a Cap device should have the best coverage when mounted on the ceiling at the center of the area to be covered, the Wap when it is placed in a corner of a (squarish) area to be covered.
This is in theory (largish empty square area with no obstacles) in practice this is not entirely true inside a house as there are also reflections of the walls, of the floor and of the ceiling, furniture, etc..