I am not actually very spring-ey at the bottom of a squat,,,because I haven't typically experienced such a great benefit from eccentric pre-load).
Squat Stretch Reflex
One of the keys to Squating more weight is to elict the "Spring-ey" Stretch Reflex.
The Streach Reflex provides a Rubber Band Effect with the connective tissue; once assertively stretched you Rebound out of the hole with greater force.
Research shows that up ot 18% more forces is produced when the Stretch Reflex is elicited.
Dr Tom McLaughlin's Research
PhD Exercise Biomechanics/former Powerlifter
The Last Word on Squatting, Men's Health, Seotember 1998
"An overlooked aspect of the squat is the transition between descent and ascent.
"You don't want to bounce, but you don't want to stop, either," says McLaughlin. "You want a slight recoil - enough that the change in direction utilizes some of the energy transfer in your body."
"As for the ascent, ... Where you avoided momentum on the way down, use it to your advantage on the way up. An explosive drive will provide enough impetus to help you finish the move."
I am thinking of practising some plyometric movements under a slightly heavier load, such as a a few light (25 lb) bar jump squats in the warmup.
Training The Stretch Reflex
To optimally develop the Stretch Reflex, it needs to be trained. Thus, performing some plyometric movements are essential.
1) Jump Squat are an effective method.
2) Touch and Go Box Squats with a Moderate Load (48-62% of 1 Repetition Max) and Low Reps (1-3) per Set is another.
Thus, if your 1 Repetition Max was 145 lbs, Touch and Go Box Squat with 70 to 90 lbs could be used.
Regardless of the Squat Training Load/Percentage, "The Intent" in each Repetition is to drive the Weight Up as hard and fast as possible.
That means "The Intent" is to try and Jump when performing each Repetition. Doing so, innevates and develops the Fast Twitch Muscle Fiber necessary producing more Force.
I haven't typically experienced such a great benefit from eccentric pre-load
The Eccentric Speed Component In A Max Squat
As you stated, the Eccentric Component "Pre-Loads" the Stretch Reflex.
To optimize that Stretch Reflex with a Maxium Load, the following protocol needs to be implemented.
How Fast You Lower The Bar
Your dropping down TOO fast. Dropping too fast increase the bar weight.
Speed Kills Powerlifting USA Research Article
McLaughlin
Research demonstrated that allowing the bar to drrop too fast MAGNIFIES the bar weight up to 149%.
That means if your drop too fast with let's say a 300 lb Squat, your going to encounter a force (weight load) of 447 lbs in the hole position.
It appears that you final attempt was 65 kg/144 lbs. Base how quickly that you dropped that means your Weight Load in your Squat at the bottom was around 96 kg/211 lbs.
McLaughlin's reaserch determined that by slowing the Eccentric Bar Speed down, the magnitute of the load only increase 112%. Thus, if you had slowed down your Eccentric Bar Speed, the force would have been around 72.f8 kg/160 lbs; something much more managable, especially with a "Springy" Stretch Reflex Recoil.
What You Need To Do
McLaughjlin, The Last Word On Squatting
McLaughlin...all the great squatters he's observed favor the slow, controlled descent... "You want to lower the weight slowly, even during the first six inches of the descent,",,,
"Too many lifters start the squat very quickly and think they'll slow down halfway, but the momentum of the bar increases very quickly, and they end up effectively lifting more than the actual weight. The top lifters have velocity and acceleration patterns that are uniquely geared this way compared to beginners and intermediates."
What You Need To Do
1) Slow your descent in the Squat down. In other word, ride the brakes during the majority of the downward movement.
2) A couple of inches from parallel, allow the downward movement speed to increase. Basically, you want to drop into the hole to elicit the stretch reflex.
This require practice to develop the timing and when you need to allow the Bar Speed to accelerate, just prior (a couple of inches) to hitting the hole.
With that said, your main issue with your Squat is...
How To Prevent Knee Valgus
The Importance of the Gluteus Maximus and its Unusual Role in Medial Knee Collapse
theprehabguys.com
"Medial knee collapse, also known as knee valgus, is when the knee collapses or falls inward during any sort of weight-bearing activity, like a squat, ..."
This is a good article that addresses what you need to focus to eliminated it.