That link is a little confusing. Think of it this way, the greater the offset the futher out the mounting point is and the larger the amount of wheel that is behind the mounting point. Thus the more wheel that needs to be tucked into the wheel well. A 35mm offset on a 7" wheel sticks out .591" further than that same wheel with a 50mm offset because it has that much less wheel behind the mounting point.

For example a 8.5" wheel with a 100mm offset has nearly 8" behind the mounting point that needs to be tucked into the fender.

I hope that makes it easier to understand.