First off, yes, i know that DDO is a party oriented game, however, i respect that some players prefer to play on they own time, at their own pace, by themselves. However, i have encountered something that makes trying to do this significantly harder in some cases.
i notice that casters still cast certain crowd controlling spells that are much more effective against a solo-er than a party. Most notably, when soloing with a melee (my first by the way), i got held 4 times in succession due to various kobold shamans, then died, mostly because i could not move.
So my suggestion is: Scale the proportion of crowd control spells cast by mobs in addition to normal scaling.
6 people:
CC spells= normal
Damage spells=normal
5 people:
CC spells= 0.8 times as many
damage spells= 1.2 times as many.
4 people:
CC spells= .66 times as many
damage spells= 1.33 times as many
and so on. In this way, there is less of a chance of being perma hypnotized/commanded/held and killed.