Squat disproportionately weak compared to deadlift

[matjusm]

So I've been lifting for almost 6 years now. Not properly all the time: in the beginning it was all about the machines and bodypart splits, in recent years I've moved more and more towards Olympic weightlifting.

Anyway, my gym recently had a powerlifting competition, a monthly "gym challenge" and I took part too. The thing that struck me was that I beat all but one of the competitors in the deadlift (by a considerable margin) while at the same time my squat was lagging behind the competition by some amount. Now there were a mix of different people here and the gym staff always made sure that the squats were deep enough but I just don't understand how my squat is so much lower than my deadlift in relative terms when compared to everyone else.

My best back squat at 170kg (best front squat is 155kg for reference), not the prettiest of attempts:


My best deadlift at 235kg:


That gives me a squat to deadlift ratio of 72%.

I was looking at the "Strength Standards" ratios on Exrx and somebody even put a graph together comparing them:


According to that people "should" be squatting 80-90% of theird deadlift with the more experienced lifters having higher ratios. By this logic I should be squatting some 200kg but I am nowhere near that.

Now you might say that as I go ATG then my squat can't be expected to be as high in comparison however I know that the man who took bronze in the C&J at the European weightlifting championships had an ATG back squat higher than his deadlift so I just don't see this as an excuse for me.

Strangely enough, I don't even train my max deadlift (or heavy pulls for that matter) that much but I do make an effort to train my squat heavy.

I just don't know what exactly I'm doing wrong. Any ideas what might be the cause of a disproportionately weak squat compared to a deadlift in a semi-experienced lifter?