Poor WiFi

I have a poor RSSI figures in the region of 60 - 80 and on the Door Bell itself says that it has poor WiFi. My router is upstairs and I have hardwired from the Router to dowstairs then into a TP Link Poweline Adaptor and still the quality is poor despite the Chime being 2 inches away from the adaptor and the Door bell about 5 feet. Is there a foolproof way to make tis system reliable and consistant?