That decision should revolve around the wireless site survey that was performed (assuming there was one) that would help you to tweak and dial-in the settings on the RF Profiles page. This is where you adjust things like TX Power, channels being used, (RX-SOP, if you don't know what this is, do not use it), basic data rates etc.
The only real impact you can have on clients connecting to 'closer' access points, is most likely going to be TX Power.
If they are connecting to AP1 because the TX power is sky high, and AP2 is 10 feet away, the client isn't going to move.
Clients are 100% in control of what AP they want to connect to, so if the clients are not moving, its because their in-house algorithm that says to find another AP when RSSI/SNR/Retries/Whatever hits value X, isn't hitting. Not much you can do about that other than tweak AP locations, and power. Which you should only do if you know how/why your doing it.