Cosy is NOT a good tariff if you want to run you ASHP efficiently..
Interesting discussion Paul on octopus heatpump & tariff, in particular their heatpump. https://forums.moneysavingexpert.com/discussion/6533864/octopus-cosy-6-actually-ready-for-market
I’m not sure why anyone would consider the Cosy 6 ASHP its one one the worst performing units, stats on MCS website.