okay so I just came back from the gym (video's are still uploading) where I tried to lean ov3er more while keeping the balance over the middle of my foot. And guess what? My back started to round. At this point I would be really happy to receive an answer to my previous question i.e. how one would assess whether a lifter just cannot assume the correct position due to mobility issues. I am seriously taking into consideration that this might be the reason why I am struggling so hard with this. (I'll upload the clips later but there's nothing new to see on them).
So here's one set where I took of the OLY shoes to see whether that may make a difference (the reasoning was that basically the shoes allow for more forward knee travel and since that's the problem I thought it might not hurt to try without them):
YouTube
I think that a couple of reps have significantly less knee-slide. However the lower back is rounding and the reps are nowhere near deep enough.
YouTube
This one's with the shoes on - reps 1 and 2 are not what we're looking for. I think in 3-5 I rather suceeded in leaning over more. But again losing tightness in the lower back.
The reason why I am so sceptical about this form is also that I'm used to squatting substantially more weight - this is 80 KG and 5 reps really messed with me. No way I could have loaded more weight on that bar.