Without seeing the exact details (i.e. a packaged workbook), it is difficult to be precise. However, the INCLUDE LoD is affected by the fields in the view. If they change, the result will change. It is probably giving you "averages," just not the averages of the values you expect.
If you attach a packaged workbook (.twbx), we can probably help more. If you have confidential data, please see Anonymize your Tableau Package Data for Sharing |Tableau Support Community.
As Bill mentioned, INCLUDE will be impacted by other dimensions you have in the view. This is because of the order in which LOD expressions are processed. I think what you are after is FIXED. I'm still learning LOD calculations, but without a few more details it is difficult to say for sure.
Hope this helps