The book is right. Two inches high at 100 yards makes it a leg-breaker at 400.
If the poster was getting higher hits at 200 yards than the book says, then it might be due to this. I have often seen people sight in their rifle at 100 yards, being very relaxed and looking straight through the scope from the bench. But when the target gets moved out to 200, they tense up. The bullseye looks much much smaller. They tend to "squinch" up closer to the scope, trying to see the target better, and thus raising up the muzzle of the rifle a tad. Often, they have also changed the position of their sandbags, to make it more comfortable to shoot, which also changes the original point of impact because they are moving their heads from their original shooting position..
Main point here is this: The .35 Whelen has never been regarded as a flat-shooting long-range cartridge by any reputable expert. It is a power house round for taking big game out to 250 yards. Back in the early 90s, when there was the sudden revival of this old round, I read everything I could on it. And range limitation was always mention as one of the few negatives of the cartridge.
The Whelen cannot shoot as flat as a .308 Winchester or .30-06. And 400 yards is really pushing it on big game for these excellent rounds. That 35 caliber pill is slowing down much faster from wind drag than the .30 calibers.
Best, Mannyrock