Ratio of distance between mirror and person

In perspective of a given example, if a man was to stand $2\ m$ away from a mirror which was $0.9\ m$ in height and was able to see his full reflection, what would the height of the mirror have to be if the man was now $6\ m$ away from the mirror and was to maintain a full reflection? Would the mirror be equal to or less than the original height and why? This scenario seems to have caught me out multiple times. So, some reasoning would be much appreciated.

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You haven't said what the condition for the height the mirror would have to be is. Perhaps the requirement is that the man can see his full reflection? This is not an uncommon example problem in geometric optics and the answer is slightly surprising but very easy to get using the rules of reflection. –  dmckee Feb 15 '13 at 20:47
Ah thank you for pointing out that critical fact! Post was edited to show that requirement –  Jared Ping Feb 15 '13 at 20:49