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