I'm in a similar setting to you. Here's my takes:
low to high is usually called short to long here. One begins with acceleration & short speed endurance -> max velocity -> longer speed endurance -> special endurance I & II
high to low is called long to short. For the 400, one would begin with longer over distance runs and extensive tempo and gradually decrease the volume and raise the intensity the intensive tempo runs and add in really fast work nearer the end of the season.
I've seen ends to the middle used to describe a program in which the speed work is short to long while the tempo work is long to short. This is what I'm using with my group. In the past couple of weeks, our speed days have focused on acceleration and either short speed endurance or short ins and outs. Our tempo days have been all extensive (75%) and the 400 guys will reach 3000m volume per session next week. After two weeks of that, we're going to start running fewer reps at a faster pace on the tempo days which will lead to true intensive tempo sessions later in the season.