OK, in theory...
A cycle should last 12 hours. Hopefully, the AMPS and the PMPS would be roughly the same number, with a nadir right in the middle at +6. As his condition improves, you'd get lower and lower numbers across the cycle, but you'd still have that nice smiley shaped curve with the ends about equal, and the nadir the low point in the middle of the curve.
A long cycle would be one where you see a later than normal nadir (by a couple hours or more) and a number at PMPS that was significantly lower than the AMPS was, like the cycle wants to run for 14 or more hours long instead of just 12. This can sometimes be an indication of a dose that is too high, or sometimes it's "just cuz" and you shrug your shoulders and move on.
A short cycle would be one where the nadir happens much earlier, and by say +8 or +9, the BG has already come up to where you started the cycle. So it looks like it only lasted 8 or 9 hours, with a nadir around +4 or so. This can happen if the dose is too low, or again, "just cuz". It is also sometimes called "BIPO" (big insulin poop out).
so in theory, you might be able to cause a "short cycle" by reducing the dose, and if you can do that, it works well when your shot times are going to be less than 12 hours apart.
Carl