Well, we’ve always known Wally’s perspective is a little warped.
Things appear smaller when farther away because their angular diameter decreases. This angle is if you imagined yourself a point, and two lines were running from that point to each side of the object you were looking at, creating an angle. Scientists use angular diameter to measure the size of objects in space, but of course the formula is based on the distance they are from earth.
Angular diameter would not help Wally at all because apparently he has absolutely no depth perception.
NOTE: If Wally & Osborne were animated, it would have been fun to have captured Osborne’s little waddle there.