" In other words, a 2-liter pop bottle shouldn't be killed under the door."
Is that an empty or full 2 liter pop bottle? If it's full with the lid on you would be right. If it's empty without a lid and the door is set to retract properly the plastic bottle will BE CRUSHED when adjusted to Sears specifications. I read the instructions. I recently installed 2 of Sears garage door openers.