I'm not sure these are the right words to some, but I'll use an example from my personal experience when I try to describe my take on all this. I don't talk about it much, but something tells me that this is the proper place.
A number of years ago, when halfway between consciousness and oblivion after major surgery, I was visited in the recovery room by two longtime training partners, both medical professionals with the credentials to get in to see me. The first was my Aikido teacher, who is a dynamic, high-output person. I immediately became aware of the energy he was giving off. It was like a man with a bucket, splashing it everywhere. The second was a fellow Aikido yudansha, who has been a Tai Chi instructor for many years. His energy was markedly more reserved, quiet and focused, yet irresistible, much like a river flowing ever-forward. Their presences and essences were both so supportive and bracing, yet so markedly different, that even through the drug-induced haze and the disruption to my own energy caused by the invasion of my body during the surgery, it made an indelible impression on me at every level. It awakened in me, if only for a brief time, an awareness and sensitivity that I have tried to recapture in the dojo (with only limited success) for the years following the incident. I was able to describe, in great detail, everything and everyone that entered that room during that time, to the incredulous amazement of the nursing staff, who kept pressing me for details of the experience for many days following. I am classically trained as a scientist, but I have been at a loss to explain any of it scientifically. But I can tell you this: It changed me and my perception of ki from that day forward.
Now, when I try to rationalize and explain what my concept of ki is, I say that it is energy borne of one's connection to the Earth, but reflecting each person's essence, personality and even their experiences. And I look at the extension of ki as the focus and alignment of this energy, and it's direction outward on an almost unconscious level, like a sprinkler shooting water. The sprinkler doesn't produce the water itself, nor can it really stop the water from flowing, but it can focus the water, and feed from it as the source of it's own motion. And the water is irresistible, with incalculable power (evidence the Grand Canyon). And the water doesn't disappear once it is "extended", it simply resumes it's place among all the other water, until it is used again.
It's the best analogy I can come up with, and obviously everybody's mileage may vary. I hope this weird experience strikes a chord with somebody, rather than making me sound like a raving lunatic.