Standover height is not the only thing you need to consider when trying bikes, top tube length, femur and arm length is important as well.
Were the 2 bikes you tried the same brand and model? Bike companies measure differently so a smaller bike from one company may be similiar in geometry to a larger sized bike from another company.
Here's a good article on how to properly fit a bicycle.
http://womenspecific.com/cycling/35/...men-specific--