First, good video. Your son has good fanning motion. Good grip too, looks like fingertips.
You know what may be the cause- 2 things.
1) Channel size. Try a smaller channel than you think you need.
2) Travel Stroke. 0:01, 0:07, 0:11
As one travels up, what is happening to the rubber? Drying off.
Great for standard squeegee.
But what does the LQ like? Wet wet wet.
Try this: Instead of traveling up ALONG the soap, travel up THROUGH the soap. Wets the rubber as you travel.
- smaller channel
- sides first
- cut through
- hanglide middle to closeout