Imo, it has little to do with the geolocation of the proxies. I think jagex is likely flagging IPs based on the ASN, basically they can check who's announcing the IPs and based on that they can flag IPs. Some IPs are clearly recognizable datacenter IPs, while some are not. However, I think datacenter IPs are okay as long as they are not dirt cheap (which leads to bad reputation and abuse -- if too many people on the same subnet bot runescape then something's off with that whole block of IP)