I guess I missed the recent thread where this topic was brought up, but I'm here to answer it now.
First of all, there's absolutely nothing wrong with switching the 10x3 and 5x10 lower body methods so that the Front Squats are performed with the 10x3 method. But for those who are planning on performing the ABBH routine for 6 weeks, the problem is unavoidable (since method/planes need to be switched for a subsequent 3 week continuation).
I recently received an email from a T-reader who sent me a quote about the 5x10 technique being, well, stupid. His reasoning was based on something Poliquin once said about the "scapular retractors" not possessing the necessary endurance to perform Front Squats for anything more than a few reps - complete bullshit. If the scapular retractors couldn't possess endurance capabilities, then no one would be able to perform 30 pull-ups (not even 20 for that matter). So let's throw that statement out the window.
The scapular retractors are rarely trained isometrically for any length of time. Therefore, when a trainee performs Front Squats for more reps than they are accustomed to, the scapular retractors fatigue out. No problem, this is what training is all about: force the muscles to adapt. Within a few weeks of 5x10 Front Squats, fatigue of the upper back musculature subside due to isometric/endurance adaptions. There's no need to avoid the issue.
But, then the issue of technique arises. Unfortunately, I can't describe the perfect Front Squat technqiue via computer, it needs to be seen in person. But here's what you should keep in mind:
1) You should cross the arms and wrap your thumbs underneath the bar (the traditional Olympic style technique is too demanding on flexibility for most people so I'll avoid describing that technique).
2) You must keep your arms/elbows elevated as high as possible. This is imperative.
3) You can elevate your heels on two 25 lb plates in order to keep your torso more vertical (i.e. less upper back tension needs to be maintained since your torso isn't leaning forward).
4) You can purchase a Sting-Ray device that rests on your shoulders so the bar can rest in it (the Sting-Ray is the front squat version of the Manta Ray).
5) You can roll a towel around the bar so it doesn't dig into your anterior deltoids, and it will provide some resistance against rolling.
Now, back to the issue of TUT. I recommend a 101 or 201 tempo for the ABBH lifts. Therefore, each 5x10 set should last 20-30 seconds. Poliquin often prescribes a 402 tempo for 3-5 reps with the front squat. If you do the math, you'll quickly realize that I'm not forcing anyone to perform the front squat for any TUT longer than what is typically prescribed. The only difference is the number of reps.
Bottom line: switch Front Squat method to 10x3 or force those endurance-lacking scapular retractors to adapt (I prefer the latter option).
Hope this helps.