I suddenly was getting confused while reading about inductors. The formula for inductance I was using was the one like in the answer to this question. However, I have also read that the inductance of inductors in series is the sum of the inductances (like with resistors in series), but that suggests to me that longer inductors would have larger inductances. The formula in the link has length on the bottom. I'm probably missing something simple here but I'm not sure what.
The answer you linked describes the effect of spacing out the windings on the total inductance. That is,
length refers to the length of the solenoid, not the length of wire used to create the windings. Consider: