Your quote is not too bad. However, try Sovereign (a broker), through whom I am arranging insurance at present underwritten with Legal & General. My position is a little different to yours - perhaps even harder to insure (?) - I wanted cover notwithstanding being PPL, up to 100 hrs per year including aerobatics and formation flying. Their Illustration is reasonable (comparatively speaking that is...)
Maybe they can assist you. Phone 01292 880074, ask for Nigel Howard.