There are a lot of variables besides scope settings involved.
Something as simple as letting the cartridge lay out in the sun and get hot can change the point of impact quite a bit. Another is how long you leave the cartridge in the chamber before shooting. If the barrel is cold, it will keep the cartridge cool but if the barrel will heat up it will warm up the cartridge. Some long range shooters keep their boxes of cartridges in a cooler and do not let them be in the chamber for more than 8 seconds before firing the shot in order to minimize temperature variables.
Are you shooting down near sea level or way up in the hills? Are you shooting with the rifle level or is it inclined? If it is inclined, the trajectory must be adjusted for at long range.
How temperature sensitive is your powder? You can only know by loading up a box of ammo and then testing it at different temperatures. I loaded up 50 rounds during the winter, shot 10 across the chronograph, then shot an additional 10 at varying temperatures. You would be amazed how much difference that one simple test makes with regards to velocity. A nice sedate winter load can end up being a realy hot summer load.
How much shooting have you been doing at known distances and conditions to verify actual settings under real world conditions. Computer programs are only as good as some geek makes them and only give good output if you have good input.
You need to do a real world log book. If you don't have one, go to this link and print out the pages you want to put into a notebook to give you ready access to real world data. The log book is called Tactical, but is really excellent for any sort of field conditions.