With a large size tissue box, when it gets below about half full, the tissues often do not dispense correctly, frequently dropping down inside.

The cause is that that it's too far from the top of the stack to the box opening, so pulling one tissue out does not always fully engage the next tissue.

To use:  When the box is about half empty, turn it over, open the flaps on one end, and insert this riser, flat side down against the tissues.  Tape the flaps closed again, and you are ready to go.

Note:  I designed this for a Bambu A1 Mini so it is shorter than the box.  On a larger printer it could be made a little longer, but it's not necessary.  It works fine like this.