Tuning a rocker

A friend has just acquired a S/H rocker. Not a bad looking piece and will be nice when restored and re-upholstered. However it's quite uncomfortable! When sitting in it and "balanced" without moving, you're in too reclined a position for comfort.
How can I adjust this thing ? I'm thinking about either taking the legs off the rockers and moving them backwards, or maybe by lifting them with a leg extension under the back leg. How does one "tune" a rocker? How do you decie what's the best position for it, without sitting in the thign for 6 months?
It has been suggested fitting a wedge underneath the rear of the rocker would do it, but I think the real problem here is how to "move" the rocking position, not to "limit" it.
Thanks for your suggestions.
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