Addional jpg.files for cover art do not show in correct order?

I regularly add addional cover pictures (back cover, booklet, …) by putting the jpg.files into the album folder. I try to give the correct order by the naming of the files, like:

Sometimes Roon decides to show these files in a different order. I do not understand why? Is this a matter of file size? How can I get Roon to simply show the covers corresponding to the files names?
Or what other parameter does Roon use for the sorting?