The Epson V700 scanner comes with several film holders, each of which contains plugins which seem to be intended to adjust the height of the film over the scanner glass.

I recently got a Betterscanning film holder, and using it I determined that the optimal height of the negative image over the scanner glass is approximately 3.5 mm. But to use that film holder I have to tape the film to the glass. For many purposes, it will suffice for me to use the 4 x 5 film holder provided with the scanner. Using a digital dial caliper, I can set the height of the film in such a holder to what I want it to be and I can get it pretty close to that measurment. But I don't see how to adjust the positions of the plugins. They seem to go into the holder in only one position.

Can anyone tell me how they are supposed to be used?