At the very LEAST "Learning to Live", "Lines in the Sand", "Trial of Tears", "Beyond This Life", "Home", "The Glass Prison", "The Great Debate", "In the Name of God", "In the Presence of Enemies (at LEAST part two!)", "The Count of Tuscany", "A Nightmare to Remember", "The Shattered Fortress", "Breaking All Illusions", and some others that I've probably left out should ALL be considered epics.
All of the songs that I've named are over ELEVEN minutes long, and I think it is INSANE to say that a song of that length is too SHORT to be considered an epic!
Yeah, a lot of those songs are pretty 'epic' per se, but we seem to have such strict definitions here for these otherwise very ambiguous descriptions. Most of the songs you mentioned might as well be considered pretty epic, at LEAST relative to other songs and especially other bands. But I think some of them like The Great Debate and Beyond this Life, also probably Home, I sort of consider as "long songs". They've got fairly standard structures, but generally have a heavily extended instrumental section of some sort which separates them from other standard songs. So it's sort of a case of 'One' Syndrome (Metallica) in a lot of cases. Or Endless Sacrifice syndrome in DT terms as a good example of the type of structure I'm describing. Can also be observed in other songs like The Ministry of Lost Souls, Outcry, Sacrificed Sons. A Rite of Passage sort of goes down that path too. I think that's something to do with why they're not quite in the same category as the "Mega epics" if you will. 
I forgot "The Ministry of Lost Souls" and "The Best of Times."
I don't really care for either of those songs, but being that they are both over ten minutes long, they should probably be included.
I was actually expecting a lot of people to say that I'm wrong, and don't know what the hell I'm talking about.
But you seem to understand what I"m trying to say.
However, if you were to put "A Rite of Passage" in the epic category, then you would probably have to include "pull Me Under" as well.
As much as I love both of those songs, and while some people might define them as epics, I think of them more as "extra-long singles."
I have previously mentioned that I think "Metropolis" should be considered an epic, but here I'll say not just because of it's almost ten-minute (and often a good deal longer when they play it live!) but also because of it's very elaborate arrangement, and choruses that are worded differently from each other.
But since they have so many songs that are in the six-to-eight-minute range, we probably have to use a different standard when determining what constitutes a "DT epic."
It's a tough call, but I guess it partially depends on the style and arrangement of the song being taken into consideration before one that is over eight but under twenty minutes in length can be considered an epic...and on it goes...