I wouldn't overthink it for closer ranges -
275m with my data is 1.3MIL for flat and 1.0 for -30 degrees. That is 34 vs 26cm.
Most people are very poor at judging slope - if you are not measuring it, it is probably less than you think. A scree slope is probably around 30-35 degrees as a useful reference.
If you don't have the equipment to measure, it's easy to over-correct for angle - at closer ranges (i.e. sub 400m) and not extreme angles (i.e. sub 30 degrees) you are probably best to aim "a fist or 2" low or just "take a couple clicks off" and call it good.
Poor shooting position on steep angles is probably responsible for more issues than actual ballistic effects - especially with heavier recoiling cartridges.
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