The soundstage is coming from the complete high frequency content. Flat extended high frequency will give best soundstage depth and imaging.
Sounding wide doesn't mean it's big. Like a rectangle, if the depth is zero the area is zero. Etymotic has frequency response that allows the reconstruction of imaging to be a circle or a triangle. The front imaging is one of the most solid among all headphones and earphones.Cymbals can sound very far however.
If you don't find it to be the case, there is high chance that the insertion depth is not correct or your ear canals are just not compatible to the design. Using tone generator for 7khz+ to find out, be sure to use 10% or lower volume for this test. It should be a very gentle rise after 7khz with no peaks for all etymotic iems.(some may be flat but that is not critical).In general if you find peak at 7-8khz, insert deeper, if you find the sound being somewhat veil and has emphasis at 13khz, insert shallower. Changing tips is helpful, as well as modifying the length of the stem of the triflanges(it works for those who can only insert to one depth).
Once you get a smooth high frequency response in your ear, you will find that the sound stage is really something else. It's different from other wide soundstage but unique and attractive.