It has been a long time since I used telescoping and inner covers. But, aren't there two sides to an inner cover? One side deeper than the other?
My understanding on why Inner Covers are used and how they are used are for a small number of reasons.
1. It makes getting the cover off easier since the bees will usually only glue down the Inner Cover around the edges. Usually.
2. To maintain bee space between the top bars and the lid, when the shallow side is down.
3. to provide more room above the top bars when the deep side is down, so, during the winter, the cluster can have more than bee space above the top bars.
As far as Small Hive Beetle are concerned, I don't know what kind of cover would have much effect on them other than maybe an opaque/see thru cover. SHBs don't like light.
Many of my migratory covers have a feeder hole in them. I use a piece of canvas as a sort of inner cover. That's where I often observe SHB. Under the canvas when I rip it off quickly. I don't know if that promotes their existnce or not. I don't have much of a problem w/ them when my bees are in NY. Usually only seeing them while my bees are in SC. But not much of a problem there either.