Do you know your current E2 level (Cooper usually does bloodwork at the same time as lining check)?
I did several cycles at Cooper, their standard over-40 protocol stopped working for me (graduated amounts of Estrace, ending in taking 3 pills orally and 2 vaginally each day). It only made my E2 level soar to several thousand without lining growth to show for it. Adding more Estrace did not help once the E2 level is so high already. I did eventually get 12mmTL linings on both mock and actual cycles elsewhere using a different protocol.