First off, define "range". If that is GOM range, then it reduces because it thinks you are going to keep doing that. It's logic is hard to fully understand because we don't have the code.
As far as "lowering your miles/KW" rating, here are my observations and speculations:
1. Accelerating faster to cover a set distance means that your average speed during that distance is higher. While distance/speed is a linear function, the air resistance grows faster than linear. you spend less time at 5-10, 10-15, 15-20 etc, and more time at your final speed.
2. The motor might not be as efficient at higher KW loads as it is at lower KW loads. 10 KW might provide N G's of acceleration while 20 KW might not provide 2N G's. Heat loss, converter losses etc may be much much higher at 80KW than 10KW. Could be lower too.
3. If you are "punching it" you might back off more than you need to at the final speed and trigger some regen which costs you energy. If you are slowly reaching that speed you can gently reduce positive acceleration without getting into regen.
4. If you are traveling at a higher speed at any point, the more energy you lose if you suddenly have to slow down. If those events occur randomly**, on average you will lose more energy from some events if you reach high speeds faster.
**I have noticed that traveling slower than 20 MPH appears to invite people to turn in front of you, enter the roadway etc, as going that speed or lower may be perceived as "ready to yield". Sometimes going a little faster leads to more constant speeds.