Wpa_supplicant, client not automatically roam to new AP

I am using wpa_supplicant for wifi client, try to roam between 2 APs. the roaming is working, but it is very slow. It seems it only roam to new AP until lose beacon, or signal is very very weak. I want to make client automatically roam to new AP when the received RSSI is below certain threshold value, for example, -65dBm.
currently I am using wpa_suppliant bgscan, it seems not working as I expect.

bgscan="simple:5:-60:60"

refer below, signal is lower than -89 roam to AP2, I expect below -60, should roam, but not

bssid=AP1_MAC freq=2412 ssid=test RSSI=-90 NOISE=-104
bssid=AP1_MAC freq=2412 ssid=test RSSI=-89 NOISE=-104
bssid=AP1_MAC freq=2412 ssid=test RSSI=-89 NOISE=-104
bssid=AP1_MAC freq=2412 ssid=test RSSI=-89 NOISE=-103
bssid=AP2_MAC freq=2412 ssid=test RSSI=-43 NOISE=-103
bssid=AP2_MAC freq=2412 ssid=test RSSI=-44 NOISE=-103