Its very simple Pharphis why. Lower kurast chests drop from the line Act 3 (H) chest B, that line has runes 15 assigned (Sur, Ber) on all versions of diablo 2. alvl doesn't mather if something is softcoded in a treasureclassex line. ROF chests have runes 16 assigned thats why theoretically they would drop up to Cham. (But that doesn't happen). The only thing alvl does is increasing the ilvl to that number (and on 1.10+ also increasing monster levels to that number). Allvl does come in play in order on what magic prefixes and sufixes can spawn on an item dropped from the chest.