25% would be quite extreme. There is some evidence of that much loss on individual rows being possible, but not the entire headland. 10% is considered to be more typical, which works out to be around a 4% loss across the entire piece. Which is well within the normal range of field variability, so it is ultimately not noticeable.
Of course, if it were a 5 acre field, with some assumptions about its shape, we'd only be talking more like a 2% loss across the entire field. Not nothing, but terrible...?
Year-to-year variability will see much larger swings than that. If that's the margin you're trying to operate on, I dare say you're cooked, even if your fields are large.
