The best approach to improve the behavior of sticky clients is to enable Smart steering.
Smart steering is a feature equivalent to the RSSI threshold feature of Zyxel's non-nebula APs, where the AP will stop respond or disassociate the client if the RSSI of the client reaches a certain value to encourage the new association to another AP.
How to configure:
Go to Client Steering page, located in
Access Point > Radio > Smart Steering
Next, toggle on the Smart Steering feature and set up the Roaming thresholds to your needs.
We recommend the following values:
Station Signal Threshold = -75 dB up to -82 dB
Disassociation Station Threshold = -80 dB up to -90 dB
This should allow the access point to guide sticky clients into associating with nearby APs with better signal strength.