Modelling and I-beam using plate elements

For a 30m single span pin-roller beam, subjected to a uniform load of 25.4kN/m, the theoretical deflection is 218mm.  I ran two models.

Model 1 - Single line beam elements, Model I-beam Rev2 attached.  The deflection is 218mm which matches the theoretical answer.

Model 2 - I-section using plate elements.  The deflection is 194mm which is lower than the theoretical answer.  Why is this model stiffer than Model 1?  Model I-beam Rev4 attached.  

I would expect Model 2 to give the same deflection as Model 1 and the theoretical answer.

communities.bentley.com/.../I_2D00_Beam-Rev-2.stdcommunities.bentley.com/.../I_2D00_Beam-Rev-4.std