rad in SIO2object

What is parameter rad (float) in SIO2Object struct ? I think that it's radius , which stand in logic panel in Blender (bound's radius), but if I set 1.0 radius in Blender , in sio2 I have 1.7 value (in other sample 0.5)

It stand for the radius of the bounding sphere of the object that is calculated dynamically at export time, it is not the radius used in the logic panel. It is used for clipping as well as for certain physic bound shapes. If you dynamically scale your object you should recalculate this value in order for the default clipping algorithm to work properly.