When exporting a model, Engineering Solutions always tries to use the greatest precision when writing real numbers in small format. There are options in the Solver Options dialog that allow you to control precision and accuracy of the model.  

The Remove ‘E’ from real values option does just that. OptiStruct and Nastran solvers do not require explicitly writing an E to recognize the proper exponent of a real number and removing the E allows one more digit of precision to be included. For example,  -1.12E-7 becomes -1.123-7.

The Zero tolerance option allows you to enter a value by which the absolute value of each real number in the model that is less than this value will be written out as zero. For example, if the Zero tolerance = 1.0E-12, it means all real values from -1.0E-12 to 1.0E-12 will be exported as 0.0.