I’m still a little concerned that your actual experience in the field has you dialing 5 clicks more than the calculator says you should. You need to figure out what’s going on here.
As mentioned by 4ohSick, there’s no need to dial for distances out to 300yds. You should almost be able to just look and know that it’s close enough to simply point and shoot. It pains me to see someone range an animal well under 300yds, then dial and hope that during the process the animal doesn’t get away. Just the other day I saw a guy range an animal that was looking right at him and at risk of escaping. Range turned out to be 240yds. Then he dialed. I thought “are you serious? I’d only HAVE to dial 3 clicks, and without dialing I’d only be 2” low. Just SHOOOOOT”. Certainly there are some low velocity cartridges out there that would be exceptions, but for most centerfire rifle cartridges there is no reason to zero closer than 200yds, and very little reason to be dialing closer than 300yds. Somehow I can still find ways to screw up, but ranging and dialing inside 300yds would just give me even more ways to screw up.
You still need to figure out why you were dialing 18 clicks to be on target at 300yds. Was your 100yd zero wrong? Was the range wrong?(closer to 350yds than 300yds) Is your scope mounted at a different height than the calculator was set up for? Something is amiss.
If you sight in a 30-06/165's in at 100 yds, it's 18 clicks to 300. My .280 Rem with 150's is 17 clicks to 300 with the standard CDS system (not actual custom) and a 100 yd zero.
With a 200 yd zero, you'd only be 6-7" low at 300 with a 30-0/165's