I don't consider sdoit to be an epic but rather a collection of individual songs
A Mind By Itself is individual songs, SDIOT is more of a single song than SFAM (even though that both rave run-in tracks).
With SDIOT you just have to break down it's structure (aside from just listening to it) to see that it is one piece.
The Overture has all the major themes which are churned out again and again and again through all the movements.
About To Crash is the bookend, upbeat "home" area of the song featuring several themes which are revisited later.
WIMH/TTTSTA is a bridge section which contrasts ATC and reprises/variation more themes from the Overture in a developed fashion, TTTSTA is also a variation from the middle of ATC.
GK is a second bridge which contrasts the previous and is likewise (as with WIMH/TTTSTA) is a variation on certain portions of the Overture, and with the guitar solo reprising a theme from the Overture.
SS is an upbeat breakaway point (my least favorite part of the song mood-wise) which serves mainly as a transition back into a developed version of About to Crash.
The ATC reprise is not just a reprise of it's name sake but containing elements of GK and SS, and a direct restating of parts of the Overture with the full band, followed by a reprise of WIMH.
Whereas Loosing Time/Grand-finale is a variation and development of a certain melody and progression that occurs not only in the Overture but in ATC and GK too.
The song of SDOIT is not a single story, but then the only DT epic that even tells a story is ITPOE. All other DT epics are more loosely relating themes and philosophies.
Moments from SDOIT can be played live separately but they only work with reference to the song as a whole. It contains no standalone movements.