I would first check the transmit power threshold you have configured on the controllers, using the 2 commands shown here, there is a good possibility that because of the distance between the AP (especially with out knowing if there is anything between the AP's) that they are seeing each other so strong that they have to turn the power way down as a result. This could be tweaked some using the Tx-power-threshold settting. This is common and proper behavior. See the commands below and some sample output.
show advanced 802.11a txpower
Automatic Transmit Power Assignment
Transmit Power Assignment Mode................. AUTO
Transmit Power Update Interval................. 600 seconds
Transmit Power Threshold....................... -70 dBm
Transmit Power Neighbor Count.................. 3 APs
Min Transmit Power............................. -100 dBm
Max Transmit Power............................. 100 dBm
Transmit Power Update Contribution............. SNI..
Transmit Power Assignment Leader............... wlc-2 (x.x.x.x)
show advanced 802.11b txpower
Automatic Transmit Power Assignment
Transmit Power Assignment Mode................. AUTO
Transmit Power Update Interval................. 600 seconds
Transmit Power Threshold....................... -70 dBm
Transmit Power Neighbor Count.................. 3 APs
Min Transmit Power............................. -100 dBm
Max Transmit Power............................. 100 dBm
Transmit Power Update Contribution............. SNI..
Transmit Power Assignment Leader............... wlc-2 (x.x.x.x)
default now is -70dbm which means that the ap's will turn down their power until their neighbors hear them at a -70 signal.. You may need to change this to -65dbm but be aware that this could cause more co-channel interference depending on where the next ap on the same channel is, this setting is also global. The other option you have in the newer code is the set a minimum and maximum that the RRM system will allow, here you see they are set at -100 & 100 respectively. You could try setting the minimum to say 12.5 dbm which is like power level 1 or 3 depending on the radio, band, channel, modulation, etc.
Lastly keep in mind that it could also be a client side power issue, since the communication to the AP has to be a two-way communication; which means if your client has a maximum transmit power of say 25mw or 14dbm, then having the AP push out 50mw or 17dbm of signal is useless since in many cases the AP can reach the client device but the client device won't be able to talk back
