I'm not trying to start an argument. This is definitely a positive bet. I understand the calculation for what you call risk/reward. The important thing here is understanding how to use the push chart to understand that it is a positive bet.

I'll add a couple of comments that someone might find interesting.

Not all middles are profitable. fav-1.5 and dog+2.5 is a middle around the 2. This not betable because the 2 doesn't hit frequently enough to cover the cost of the juice.

3, 6, 7, 10, and 14 are called key numbers because these are the most common margins of victory. Middles around these numbers are potentially profitable. Bookies are reluctant to move lines around key numbers because they don't want to set up middle possibilities. In the modern era bookies use the juice to adjust the line. You might see +3-110 at one book and +3.5-130 at another. These are the same line. You gain 1/2 point but the bookie maintains his advantage using -130 as the juice. (-130 is for illustration, I don't remember the exact number).

Chances of finding a middle like above in the real world are basically zero. Bookies don't allow them. There are many people (and bots) looking for this sort of thing. If one were to appear it would be bet out of existence almost immediately.