Once it gets close to 20 feet, you would have to regularly prune it to size or try pinching it in Spring after leaf out.

But those wooden fences though, they have to be replaced every now and then. I would hate to have CH swallow the fence and then find that the wood fence is deteriorating and that you need to replace the fence and prune CH down to a smaller size. Was the fence recently built?

Yes, fence is less than 1 year old, and 6x6 posts, so I expect it to last some time.

And since I need more width than height, do you suggest I plant in middle of the area? Train sideways and cut top once it reaches the height of the fence...

If the sun strikes it equally at all times, that would be fine.

I have a climbing hydrangea that was growing on a trellis in my back yard, and the trellis had to be replaced with a newer, heavier wood trellis at about the 10 -year mark. I had been attaching the emerging branches with twist tie through the years, and when it came time to take the old trellis down I just untied the twist ties and gently laid the vine down on the ground to one side, with some trimming and accidental breakage inevitably occurring. My CH had taken 7 years to bloom, so I was very careful with it and so were the landscapers who were ripping out my flimsy trellis and replacing it with the sturdier one. Needless to say, they were careful not to step on the resting vine while they worked, and yes there were a few accidents where some branches were lost. However, once the new trellis was completed we just re-tied the surviving branches in a nice spread out pattern (we did not remove the plant, just re-tied) and for the rest of the season it resumed life as if nothing had happened. I made sure it had sufficient water, kept an eye on tying newly emerging branches, and on the 2nd year now it looks like it's been there forever and I'm having to cut back again. They are quite resilient! I don't even always remember to fertilize, but that plant is going gangbusters again.