Welcome to the forum. Where an image is sorted in the LR Grid view or filmstrip is entirely dependent upon the sort order chosen for the folder/collection that you are viewing. If the sort order is filename or capture date, the PS derived image will show up in the grid near the last source file. If (as in the case of some special collections, the default sort order is "Added Order". then the PS derived image will show up at the end of the list, For several (all?) versions of LR, I have always had to deal with the PS derived image showing up before the last source image. This is I think primarily because I always sort on Capture time, and the PS derived image will be assigned a capture time of the last image. If the PS derived image file name is based upon the Source image(s) with additional characters added, then Filename sort order will determine whether is sorts before or after the last source image.