This is what middling math looks like to me. According to this chart, when a team is favored by 3 points the favorite will win by exactly 3 points 8% of the time..

So you see the consensus line is -3. But there are a couple of outliers. One book has the game at -2.5 and another books has the game at 3.5.

When you shoot for a middle you bet 11/10 on both sides. You put up 22 units but one side will pay 21 units so you are essentially betting just 1 unit.

8% means the game will middle 1 in 12.5 attempts.
When you cash both tickets it's a 20 unit win.

That's an EV of 160%. That's a huge edge.

But what if the calculation is off. Say it should be 6% instead of 8%.
The EV would be 120%.

So it looks like the middles carry big edges. You just don't get to cash a ticket every time.