Alright, so a skim through BASL let me find this statement in the Hip External Rotation with Flexion – Option 2 chapter:

“This is the first mobilization that I recommend to people who experience lateral knee pain in the first position. If you’re so tight you’re not flexible enough to get your knee to the ground, you end up pulling your lateral knee joint apart as you load your leg into flexion. By posting up on your foot and then letting your knee drop out to the side, it solves a lot of the knee-gapping issues that causes your knee to flare up. Not only that, the position is much easier to get into because you’re not as restricted by your back leg in extension.”

Later, this:

“There are a lot of athletes who are so stiff they can’t get into any of the previously demonstrated positions without their knee joint ripping apart. If you fall into that category, you need to address the stiffness with some quality quad and hip smashing, and you need protect your knee joint by dropping your foot off a box.”

This seems to be the problem. Stiff hips, so the torque is instead be translated through my knee and opening up the LCL. The workaround seems to be to drop the foot off of the box (if elevated) or cradle the knee towards you to alleviate it. That’s fine, but that’s alleviating symptoms—I need to address the cause, which (again) I assume is tight ext. rotators and hip flexion. This makes sense, cause I’ve been having trouble getting my knees out in the squat lately.