I believe about the time that Honor explains to her crew, after going through the rapid-fire
captain to captain talk with Caslet the fiddly bits were mentioned.
From the wiki, which is also in that boiled down chat...
The Selker Rift was a hyperspace rift about twenty light years short of the Sachsen System.
It was essentially a volume between two prominent grav waves. It was unavoidable for starships traveling between the Anderman Empire and the Silesian Confederacy on the Triangle Route. Most ships crossed it under impeller drive at a speed of .16 c to allow them to dodge a dangerous rogue wave known as the Selker Shear. This extended the travel time through the rift to about five t-days, leaving freighters exposed to piracy.
In 1910 PD, the Battle of the Selker Rift took place in the area. (HH6)
So ships travelling the Selker Rifts, are doing so on impellers although this could be interpreted as strictly non-hyper, ships do travel outside of the waves. The reason most travel is done along the waves, include faster, less fuel, and less wear and tear to ships & crew for crossing Alpha wall.
Other notables:
-the Selker Rift has rather low 'particles', which gives ships a much longer sensor range than usual in hyper.
-not being a grav wav, sidewalls, missiles, LACs, decoys and escape pods can be used without being instantly destroyed the moment they leave the 'safety' of an intact sail-using ship.
Another great example of this, is one of the battles of Hancock, Second I think, when the original Shrikes were hounding the Havenite Battleships. The Peeps knew that the LACs were only firing those grasers into them to cripple their Alpha nodes, and would instantly cease attacking a ship as soon as an Alpha was destroyed. The chasing superdreadnoughts could then flick up into hyper and drop down right on top of the battleships, regardless of any other distance or escape maneuvers used by the battleships.
And a great counter-example of not being able to escape without intact (with alpha nodes) ships, would be when Honor had to cut and run from Michelle Henke during one of the Cutworm (or similar) offensives during the Second War (Solon I think). Michelle's BC(p) suffered alpha node damage, and the system in question was in the middle of a grav wave. So the ONLY way to escape was to use sails, and prior to the surprise, Honor had been musing that she was
uncomfortable attacking this particular system, and attributed it to the the grav wave-only escape. And another tidbit from that same thought is that most admirals seem to be more on edge when attacking those types of systems, because it becomes a "win or lose heavily" situation.