The DayZ CLE as it currently stands does not allow you to fine tune the balancing of item spawns when the item in question is used in multiple tiers.
For example, if I spawn an M4A1 in Tiers 3 and 4, I don't have the ability to make more of them spawn in Tier 4 than in Tier 3, its shared across the two depending on other items in the tier, open spots for loot, etc. You can kind of fudge this a little but as server developers we don't have fine control over this.
I propose breaking out the CLE algorithm to accommodate multiple declarations of the same item in types.xml in order to pick up different nominals/mins across different tiers. I.E:
<type name="SparkPlug"> <nominal>10</nominal> <min>5</min> .... <value name="Tier1" /> </type> <type name="SparkPlug"> <nominal>3</nominal> <min>1</min> .... <value name="Tier2" /> </type>