As others have said, find something to block the sun. I have the same issue late afternoon in my long range practice spot. If prone, putting a pack between you and the sun helps and or draping a shirt/jacket/whatever you have over you head and the scope's eyepieces. Another thing to consider...
I use Sig Kilo 3000s and they're great. I've never used the native "AB-lite" that comes preloaded in them though since I always pair them with my Kestrel 5700. That combo has given me dope that's bang on out to 1600 yards so far in all my guns.
I'm in the mountains of BC and a tripod is the key. The terrain makes it very unlikely that you can prone out. I've used tripods for years in long range rifle matches and it's just a no-brainer to bring one along when I hunt. The one I use for matches I can confidently make hits (with the...