You are confusing EQ with simple brain to body mass ratio. Small animals have proportionally larger brains because when a body part, such as an arm, is small, it take just about the same number of neurons to move it as you do a larger arm. Therefore, as animals grow bigger, their brains do not grow proportionally. Large animals therefore have proportionally smaller brain to body mass ratios. To correct for this, a more accurate formula is derived to take this into account. As the Wikipedia explains:

"Generally, small mammals have relatively larger brains than big ones. Mice have a direct brain/body size ratio similar to humans (1/40), while elephants have a comparatively small brain/body size (1/560), despite elephants being obviously quite intelligent animals.

Several reasons for this trend are possible, one of which is that neural cells have a relative constant size. As an animal's brain gets larger, the addition of more nerve cells will cause the brain to increase in size to a lesser degree than the rest of the body. This phenomenon has been called the cephalization factor: E = CS2, where E and S are body and brain weights and C is the cephalization factor. Thus just focusing on the relationship between the body and the brain is not enough; one also has to consider the total size of the animal. To compensate for this factor, a formula has been devised by plotting the brain/body weight of various mammals against each other and a curve fitted so as to give best fit to the data.

The formula for the curve varies, but is usually given as Ew(brain) = 0.12w(body)2/3."