Hi Sander,
Please can you add more detail.
-30dBm RSSI is an extremely high signal level. The closer to 0dBm when using negative figures = a stronger signal. E.g. -70dBm is a weaker RSSI than -60dBm. -50dBm is a stronger RSSI than -55dbM.
I recommend you check the AP TX power configuration in the SZ, as this can be reduced by over 10dB. Bear in mind that each 3dB is half or double the TX power. E.g. 13dB is twice the power of 10dB.
Thanks,
Darrel.