The GCI System in Use by the RAF was AFAIK never actually matched in it's technical capability by any system adopted by the Luftwaffe. In 1940 OTL the British were world leaders in the use of RDF (radar) for fighter defence both day and night. Whilst Technically British Radar was not the necessarily the best, the ability and organization to use the new technology was. The RAF are not using GCI/PPI to provide defence lines. the UK is geographically too small for that. Instead it is an integrated whole nation system.