A 3 man party is harder than other numbers of parties

I have found that it is harder to kill things, and we take more damage in a 3 man party than 2, 4, 5, 6 man parties. Not sure if this is intentional but it feels like difficulty is scaled to a 6 man party, and as a 3 man there isn't enough dps, even with a sorceress and monk on the party. (I am warr so basically we only have 2 dps). Any thoughts?