Back Angle in Squat

I have problems with keeping my back arched in the bottom of a squat. A guy in the gym told me to try and keep the torso upright to solve the problem so this is what I focused on for a while. Recently I found out that either I understood the guy wrong or he gave me the wrong advice because I squat low bar. I never knew that I should actually focus on leaning forward more while trying to maintain an arch, when I have the bar low.

I keep the bar low on my back with a medium grip on the bar but I can carry it lower when I move my grip out.

I wonder how far I should be leaning forward with the low bar position, do you guys have any advice? And should I go with the closer (little higher on my back but still low bar) or wider grip (pretty low on my back) ?

Post a vid. Although you will find a lot of opinions on this, the most probably answer is to experiment and find what feels the best and where you are the strongest.

How long have you been squatting, what is your bodyweight, and best squat performance either reps or max.

Basically you have to lean enough to keep the bar centered over your foot or you will fall over. How much lean this requires depends on bar placement, body proportions, how wide your stance is, how much you sit back, etc… Basically you need to keep your arch no matter how much you lean forward. Obviously a bigger forward lean will increase the lever arm between the bar and your hips and could make is tougher to maintain your arch.
As mentioned earlier, if you want something more specific you can post a video.