Collective position will most definetly have an effect on throttle travel. 100% at flat pitch obviously uses less manifold pressure than in the flight position so the engine fuel/air demand is less. The butterfly opens further when the collective is raised to allow more intake(That's what correlation is). When the collective is full up the butterfly is full open unlike at flat pitch.Watch the throttle arm, wind it to full throttle at flat pitch and lift the collective and see what happens. At full collective the accelerator pump also has more travel so you WILL get more fuel for priming and because the accelerator pump is spring loaded it's a good idea to pause momentarily at full throttle to let it do it's thing.
The lack of understanding of something as simple as correlation is a bit scarey. Pilots should be made to learn this **** and retain it