This is entirely correct...
U.S. TERPS is only for all engines operating. In non-mountainous areas the IFR obstacle departure procedure (ODP) is assessed out to 25 miles. In regulatory Designated Mountainous Areas (DMAs) the assessment is to 46 miles. If a 40:1 performance surface cannot be maintained in all directions, then a route ODP must be developed for publication.
The assumption: with all engines operating you will be level at a legal IFR altitude within those distances.
With OEI it becomes the operator's responsibility to assess the takeoff and en route-climb flight path. At a places such as Calgary or Denver the operator's performance department needs to design OEI routes that don't go straight-out into high terrain..
There is NO criteria for EO. NONE. Procedures that have an OEI track, rely on the engineering dept to load the ac accordingly.
The ONLY answer is that is varies very specifically by aircraft. Performance in a turn OEI is usually far less that anyone anticipates, especially when it is warm.