When creating an archive using DOpus it seems to always use default dictionary size (32 MB for RAR5 etc.). It would be nice to support higher value here for better compression. WinRAR supports up to 1024 MB, and it indeed makes a difference for low-storage but high-RAM devices, or when using cloud services.
This is the command-line option to use: Switch -MD<n>[k,m,g] - select the dictionary size - WinRAR Documentation