I don't get why but people are so quick to judge the ROM "reduction" of the LBBS. What determines the ROM in the movement? Bar travel or hip travel? If it is obviously the bar travel that's relevant because we are interested in how far the weight travels, then why judge and compare the depths of the hips in the LBBS and HBBS as indicators of ROM?
Since the back is more horizontal in the bottom position of the LBBS, the bar travels lower in relation to the hips when compared to the HBBS. Which means you can't just say the ROM on the HBBS is longer than on the LBBS. It will probably depend from person to person and might very well be the other way around.
Here is an interesting picture we all might know:
And to be fair it's true the picture above shows a "normal" HBBS and not an ATG squat. But even then: