I test lot of cases about a slow conexion (because of weather conditions, latency, ...), but I remark if you use a DB attached to radius server, this DB can be very slow, too. It happens because the DB has a hight load or a lack of memory of the machine.
Obviously, the unique solucion to mt is to wait, so the /radius timeoute has to be hight. Above all, this high timeout is usefull for roaming services because radius server do proxy radius and some AAA servar are too far or too slow to answer. My normal time in these cases are 8 secs.