Hi @wyfy-2015
If you set the AP between 11 and 17 and client at 14 this means that the client will be between 11 and 17 right?
But the problem your are describing is quite common. AP has higher power than clients and often this can happen.
That's why when you are going to perform a site survey set the AP power to the same value of client power or even lower, so that you make sure that client's will always be heard by AP.
-If I helped you somehow, please, rate it as useful.-