Enemies will downgrade their level range, but they will not upgrade their level range. I don't know the exact level ranges, but let's say Gold Brickers are levels 10-30, and Malta is 40-50, you can force your level range to be level 20-30. The Gold Brickers will be in range, and Malta will be dropped down to the level range. If you made your level range 30-40, then the Gold Brickers would only be level 30.
Of course, Malta are already difficult at level 50, and they are even more difficult at level 20 where you don't have as many power to be able to deal with them.
I've only recently started using AE and I've run into some frustrating problems with the level ranges of enemy groups. In one of my arcs, I want to feature a variety of enemy groups on the different missions, for example Gold Brickers on one and Malta on another, but the AE doesn't like this because both groups are in very different level ranges. So my question is: is there any way to alter the level ranges of pre-existing groups so they can be included in the same arc as groups of different ranges?
In some cases you can just sort of recreate them in custom groups, but in most this is practically impossible to do so that's not really a solution.
I can't be bothered to think of something amazingly wise or witty to show how much of a genius I am, just take my word for it.