i always use a small backpack since i havent noticed much difference using a small backpack when it comes to spooking animals. i've only really noticed a difference when using a large backpack. large backpack will spook animals 180-200m away. when i'm grinding and have a large backpack, animals get spooked before i even get to my tripod. when using small or medium backpack, i can get to my tripod no problem. u should do a series on backpacks and see how it affects animals when hunting in the bushes.
