When I first saw this post I wanted to reply, but didn't have the time. The longer I waited the more the thread grew, and the more time I would need to properly address your questions in context with the other posts. Strangely enough my original thoughts did not change after reading through three pages.
1. At your weight 130 Flex is not too stiff.
2. You are asking a question with no real good answer. Instead of trying to "balance" in one part of the boot or another, following current dogma, you should be experimenting by changing your balance point, feeling what makes a difference and what difference it makes. You have to teach your self where to balance and when to balance there.
I'm no ski instructor, and I have no doubt that many of the other posters ski better than I do (especially when it comes to classical short radius turns), but I do have some experience. I first began experimenting with fore-aft balance a few decades ago in a private lesson. When the instructor noticed that I had no speed control and suggested he teach me how to make short radius turns to control my speed, I blew my chance at it, and instead told him I had no interest in learning how to ski slowly, and could he please teach me how to carve cleaner turns and thereby ski faster. It was a good lesson. He pointed out I was losing most by skidding the front of my skis at the start of my turns and I needed to pressure the front of my skis more. After working on that for a while and feeling like I was doing pretty good, he pointed out that now with all my weight forward, my tails were slipping a bit at the end of my turns. My challenge for a good many years was moving my "balance" to where it was needed at the instant, while keeping me in a position to be able to do so.
I have considerable experience on 70 m speed skis, and 13 m SL skis and many skis in between, mostly clean carved turns, although I've been motivated to learn short radius turns in the last decade or so. The same applies to all types of turns and all types of skis - Change things up and teach yourself; broaden your experience and learn from it.
When you have speed you add momentum to gravity and the forces grow exponentially (to the power of 2 actually). There are many ways to pressure the ski. The first two that come to mind, through the bottom of the foot (predominant in the days of leather lace-up boots), by levering against the front of the boot (predominant in race boots). I find it very seldom that I need to lever the boot to the extent that I take pressure off my heel, but never say never.
What matters is the net force put through the ski onto the snow and what that force profile looks like (imagine plotting x being distance from front tip of ski to tail of ski and Y being pressure), that force profile depends on many things, but you don't need to be an engineer to manipulate it. You can feel what your are doing and where you are directing that force. Ok, it helps to be an engineer to imagine the line of action of the net force you are exerting on the snow and know the equal and opposite force is accelerating you.
You need to play with directing your force more forward, centered, and more rearward and feel the difference it makes.
For what it's worth, years ago instructors following their training advocated balance on balls of feet, but today, instructors I've talked to say the word from on high is to balance through the middle of the arch. Probably due to the change in equipment (more side cut), I'll wager.
I will point out one pitfall to avoid. Many folks TRY to put their weight forward, put their weight or balance on the ball of the foot, and end up pushing themselves back by pushing on the ball of their foot. Pushing down and forward makes a skier move back, it's harder to put pressure on the front of your (generic your) skis when you (generic you) are in the back seat.
