I created a thread about revisiting the presentation of these numbers - Cleave Distribution stats are not representative of the full weapon. As a disclaimer, I posted it originally under the incorrect assumption that these numbers represent a number of targets hit
These numbers represent the ability to hit multiple targets, and only reflect the first strike in the respective attack chain, so you’re only seeing part of the picture - the first heavy attack has a low hitmass budget (using a shovel with a distribution of 1.04, I hit 2 groaners/poxwalkers in a single heavy), but the second heavy has a much higher hitmass budget that hits more enemies (5 poxwalkers at least with the same shovel as before)
The number of enemies a weapon can damage is not reflected anywhere in-game. That number is governed by a weapon’s damage profile, and determines the amount of damage/impact applied to the first, second, third etc. target hit by your attack. Using a shovel with Thrust, I can increase the hit mass budget enough to hit a third target, and the damage profile for the shovel (as seen here) indicates that it can damage up to 3 targets with that specific attack. However, no amount of power will allow me to damage a 4th target with that attack
tl;dr: Cleave Damage/Stagger Distribution have no influence on the maximum number of targets you can damage; they simply represent the hit mass budget, which is used to determine when your attack stops cleaving through targets.