Not sure why this got down voted. It's easy to see that points can be selected between two others that are parents in some cases. With mid-points, it usually mixes a fractional part like taking a midpoint 1/2 and then moving the upper bound so the next card is 2 and then moving something between 0.5 and 2. This ends up being a messier fraction.

Adding logic to pick 1 instead of 1.25 seems easy but there are a lot of edge cases and ends up creating something that is at least as complex as this simple binary tree that generates all positive rational numbers.