-20%(ish cause it's more than that amount) dps from 0-6, and -20%(again ish) from 27-35 and only 7-11% dps increase in the middle for 3-4 units of range from the special model
You're using the wrong DPS values.
Max range decreases only by about 13% (for the weapon), because the cooldown bonus from the upgrade affects the STG44 differently. And for the record in absolute numbers this is a decrease from 2.4 to 2.09, or in regards to the total squad DPS at that range it goes from 11,9 to 11,6.
The STG44 is actually better up to range 33ish, not 27, because again the cooldown bonus affects it differently.
The mid range DPS is actually boosted by 15-23% (for the weapon), not 7-11%, because again the cooldown bonus affects the STG differently.
Real DPS comparison:
https://ibb.co/6tBpsp4