I'm confused by the "you economic base compared to XXX" modifier when trying to vassalize a nation. I am frequently a very large nation trying to vassalize a relatively small nation and the only thing stopping me is this modifier. Moreover, this modifier is frequently -60 or more. From the wiki I saw that the minimum value of this modifier is -90, so I'm confused at how such a large nation can have such a lot economic base.
What do I need to do to improve this value?