In regards to cropping, read over this thread and it should make sense. The replies in this thread are by the dovi_tool developer quietvoid.
viewtopic.php?style=6&t=25163#p108250
Essentially, whenever you extract the RPU, if you cropped the black letterbox bars out of your x265 encoded video (in Fastflix in my example use case), then you should use -c switch when extracting the RPU.
If you did not crop the black letterbox bars, (or there were none to crop), simply don't use the -c switch in your dovi tool command when extracting the RPU.
So for an example:
Looking back at the full command to pipe and extract the RPU:
ffmpeg -i "D:\Rips\The Matrix (1999)\The Matrix_dv7.mkv" -c:v copy -vbsf hevc_mp4toannexb -f hevc - | dovi_tool -m 2 -c extract-rpu - -o "D:\Rips\The Matrix (1999)\RPU_81.bin"
a.) If you didn't crop the black bars in your x265 encode: dovi_tool -m 2
b.) If you DID crop the black bars in your x265 encode: dovi_tool -m 2 -c