Maybe I'm over analyzing, but I can envision several ways to interpret that. The Moon's orbit is complex. Part of the problem is that the plane of it's orbit is inclined relative to the ecliptic (planetary plane) rather than to the Earth's equator. Therefore, as the year progresses, the maximum or minimum declination on each orbit relative to the Earth's equator varies throughout the year because of the changing angle of out equator relative to the planetary plane. So one month it could be at, (just pulling out random numbers), 20 degrees. But on the next month it's 23 degrees.

Yet another possible meaning is the highest point in the sky each night - the 'high noon' for the Moon. But I doubt this.

My guess is he means the highest/lowest apparent position on the celestial sphere each orbit (month).

Again, maybe I'm over analyzing, but it's good to eliminate unnecessary ambiguity. We shouldn't have to guess. People like to deride science for the precise way it uses words, but this is exactly why - to eliminate ambiguity.

It's probably all a moot point anyhow. The claimed windows are small enough that the probabilities remain low. It's not like those folks claiming an increased quake risk plus or minus one week around the full and new moons.

Brian