Esso SpeedPass reward confusion

So we use the Esso SpeedPass thing because it's convenient, and we get free gas occasionally. Since I drive about 2 hours a day to get to and from work, this is a nice benefit for us.

My wife asked me about the actual rewards themselves, because they are quite confusing. She noticed that the point gap between the $X Free Gas cards was inconsistent:

Then she said she couldn't make much sense of the values of the discounted gas cards, either:

Note that the smallest and largest cards give the discount over 200 liters, while the medium one gives the discount over 250 liters. Also, you get a little extra if you're refilling an existing card rather than getting a new one.

So I did what any proper math-type husband would do: I put it through a spreadsheet. Before reading further, try to guess which of these rewards gives the lowest Point/$ ratio. The answer may surprise you. Note that a lower Points/$ ratio is better, since it means you get more rewards for fewer points.

Here are my results:

 

The winner is... the smallest discount card at 150 Points/$! Well, once you have one, refilling it is an even better deal, but you get the idea. Look at how what you would think would be better deals are not. I would have assumed saving your points would give bigger rewards; but it doesn't. The 25-cent-per-liter card costs you 166 points for every dollar of reward, which the 5-cent-per-liter card costs you 150 points for every dollar of reward.

Look at the Free Gas cards on their own: the best deal is the $70 one. I would have expected the $80 one to be the best deal. Here's a plot of the values with Points on the X-axis, and the number of Points/$ on the Y-Axis:

  

Look at how goofy this graph is. The quickest rewards are the worst, which we expect. Then they get better, then worse, stay the same, then get better, then worse again at the very end.

I can't think of anything else to say about this, so that's it for now.