Where is the kuzushi in osotogari? Easy - tilt them on a heel into the back corner - right? Sorta... Sometimes...
That back corner is often the direction of the offbalance in osotogari, but you remember from my last few posts, kuzushi involves three things; 1) a direction, 2) a point in time, and 3) an unintended action by uke. Saying that kuzushi in osotogari means tilting them into the back corner ignores the timing aspect of kuzushi and minimizes the unintended action aspect.
BTW - that reminds me of a joke: Q: How many judoka does it take to screw in a lightbulb? A: 5 - one to fix the bulb and 4 more to say, "That's not how I do it."
Well, anyway, "Tilt uke in the back corner and kick the hell out of his leg" is not how I prefer to do it ;-) Here's how I like to do it.
Assuming you want to reap his right leg with your right leg, move with uke and watch his right leg. Anytime he takes a step and that right foot hits the ground, pull with your right hand perpendicular to the line of his feet - a short, sharp tug exactly opposite to the direction you want to throw - enough pull to make him bobble front-to-back, but not enough to make him take much of a step. Then, as uke acts to right his posture against the forward tug, you step in and reap.
So, the offbalance for osotogari (the way I like to do it) looks like...
Timing - the instant the foot you want to reap touches the ground after a step
Direction - tug their lapel or neck forward sharply into the hole.
Unintended Action - uke wanted to take his step and end up balanced. When you tugged on his lapel, he tilted forward and had to correct backward into your throw.
Sure, this thing throws into the back corner (usually) but that is the kake phase of the throw - not the kuzushi phase. The kuzushi actually happens in the opposite corner in the front ;-)