Actually, "High angle" fire is defined as any elevation greater than 800 mils (45 degrees)... the point that any increase in elevation results in a reduction, rather than an increase in range. Very useful, though back inthe old Cold War days when there was a significant counterfire threat, many manuals argued against HA fire due to the excellent signature it gave to the enemy's counterbattery radars. Nowadays it's mostly the Air Force that complains, since HA fire consumes a lot more airspace that they can't (or at least shouldn't) fly through when a fire mission is in progress.

Tom
(former Major, 1st U.S. Field Artillery)