This would not be like a women randomly believing that she could make herself stronger if she got angry enough. What I am describing is a woman's individual destiny being that at one particular moment in her life, she will be strong enough to do whatever the Pattern needed her to do. The Pattern's most direct way to do this would be through making her a t'a'veren for that one moment. We might even see this same circular reasoning in how one gains strength in the Power; it could be said, philosophically, that individual gains in the Power are meant to make sure each individual is capable of fulfilling what the Wheel wills at that moment. You could almost attribute an almost biblical quality to what seems like a mechanical process: the Pattern gives you strength in a direct portion to what you need to accomplish in a given life.

The scene in which Rand visits Egwene in the Hall is interesting when I think of the metaphysical underpinnings of the One Power; in this moment, even if every single Aes Sedai wove a Shield and meant to hold Rand, something about his soul had changed, and they sensed it on a higher level (i.e. the Pattern). They sensed the possibility that despite all notions of reality, in that moment, he was so powerful that they couldn't hold him despite every one of them trying. Despite this, it almost seemed that his fate was in Egwene's hands, and the Pattern hinged on if she would allow him to leave or decided to hold him. Could they have held him if they wanted to? I don't think we can say his "strength", as we've been discussing it, has increased, but it seems very definitive that his channeling is much more powerful than it used to be. I tend to think that what the Ashaman saw was Rand channeling the One Power directly through his eternal soul, and only partially filtered through his body as is usually the case.

I'm not disagreeing with you, entirely: I basically don't think we can quantify what the One Power really is, and when we talk about "strength", it is something more gross and connected to physical limitations or mundane judgments (i.e. the volume, mass, etc. you had mentioned) but if the Pattern needed you to be stronger and/or on some deep level you felt that you needed to put forth all of your strength to accomplish some mission, you could connect to a higher plane of your metaphysical existence to do it. Kind of like a woman whose child is pinned under a car suddenly finding the strength to lift the car and push it away; in that moment, there was a connection between her divine, eternal spirit that exceeded height, weight, volume, etc.