Looks like when turrets rank up they get a bonus to attack speed and range, but a nerf to the damage (+1 instead of +2.1 for unranked turrets) - This is with the first technology for both physical attack damage and attack speed.

Ok I did a little more testing and if you decompose the damage upgrades via tech you get 10% damage for turrets and 10% damage for bullets, meaning that you should see 10 + (10 x 1.1 x 1.1) = 10 + 2.1 = 12.1 but instead we get 10 + (10 x 1.1) = 10 + 1 = 11.

So either the bullet tech upgrades or the turret tech upgrades aren't applying. I am speculating, but it is likely the +10% applied to the turret. I reason that the base model (which is probably untouched by the mod) receives the correct tech updates for both turret and ammo, but since HeroTurrets REPLACES the base turret with a new entity I'm assuming the +% damage to the turret isn't applying to the new entity you used. Seems like you'll need to edit the tech in question to work with the new entity you created for the ranked up versions of turrets.

Hope that helps.

+1 to this issue. Am running Rampant in my K2SE play-through and was calculating damage when I ran into the same miscalculation you did (nuclear and armored biters are SO ANGRY)

+1 on this issue. Turrets does not receive the ammo stacking bonus.