Transaction log backup after full backup is too big
My understanding is that full backups do not truncate transaction logs - only transaction log backups do (e.g., the full backup is fairly independent of the transaction logs).
However, my guess is that the re-organise all indexes does a lot of data processing - it is likely that these go into the transaction logs and are causing your issues.
You could test this by disabling or delaying the re-organise indexes one day, and see what happens to the transaction logs.