The ENS200 has a built-in directional antenna that broadcasts in the same direction that it is facing. That is the reason why the iPad gets a strong signal in the pool area but not when in the area behind the ENS200. Install an ENS200EXT or ENS202EXT instead if you want a more omnidirectional wi-fi signal.
See antenna radio pattern below:
ENS202 Radiation Pattern
ENS202EXT Radiation Pattern