I am with others that you need to upgrade your arena.
moreover DMI stands for deliberately meaningless index
here are the words of GM rip in the FAQ
"What is DMI?
DMI stands for deliberately meaningless index. It is very heavily dependent on game shape, and many managers ignore it. However, it can be a useful way to guess how good an opponent’s player’s skills are without being able to see the actual skills."
so i say you dont need to care much bout DMI.