Scan as dark as you can to get a good image for ICR as handprint tends to ne thinner and lighter than machine printed text. Scan at 300 DPI rather 200 dpi and see if that improves the accuracy. be very specific with the zone ICR rules and only specify the exact character types (digits, upper, lower etc) you are expecting, rather than using 'All'. Make sure that the ICR zones have a reasonable amount of whitepsace around them.

Direct link to FAQ