As long as the steering box can take the wheels to full lock, there is no change in the minimum turn radius.
If you mean "for a given amount of steering wheel movement", your answer is correct.
If you mean "the minimum radius that the car will turn at full lock", then your answer is NOT correct.
A shortened pitman arm results in SLOWER slower steering, but needing less effort at the steering wheel, but there is no effect on turning radius.
Regards,
Bill Lee