AD&D combat – especially initiative – is infamous for being open to numerous interpretations, and is often subject to many houserules. Demon Idol provides a clear-cut Combat Procedure, and this page provides additional rules info.

• AD&D combat is meant to be abstract. This is not a simulationist game system. There will be times you may think, “That doesn't make sense!” Just roll with it.
• This is a game, not simulation. The abstract nature of AD&D combat enables those 200 vs 200 battles of mixed troops, spells, PCs, and NPCs.
• It is only by keeping a defined combat procedure that players will be able to judge their options and make meaningful decisions. When you override rules with DM fiat, you usually weaken the game.