You cannot use BMI miles to upgrade

Have you used the timetable at staralliance.com to show all possible routes? Including Swiss, which won't show on ANA?

There are (random dates) J seats to LHR from IAD on 3 June, 8 June, 10 June etc. Taxes showing as £311 although who knows what number BMI will pick, plus of course the taxes on the TPA leg. These are on the Lufthansa flights so they will be showing on ANA - are you using it properly?

Lufthansa and / or Swiss also has J seats available Miami to London via Germany on pretty much every day in June. This is probably easier than going through IAD.