Does the void behind mean the window behind it, the larger space for activities behind it, or the aisle behind it? If the seat next to the window behind you is empty but full, it is actually a good situation.
The former two can enlarge the stone behind the back as a backing. The latter is restricted by circumstances and it is inconvenient to place large stones, or what should we do if we cannot change to a high chair because of our low position? Then you can make your own backing. For example, as mentioned above, you can put a piece of brown or yellow clothes or objects such as a pillow (that is, a pillow). If you are afraid that the effect is not enough, you can put 8 small stone springs inside the clothes or the pillow. , then it’s foolproof. This is how I handle it, haha!