this performs scale first, then moves to final position:
Code:
Vec local_anchor=EffectMesh->box.down();
Matrix m;
m.setPos(-local_anchor);
m.scale(Size);
m.move(local_anchor + pos());
If you don't want to play with 'anchors' then you can just translate your mesh in Mesh Editor so it is not centered, but located above the "identity matrix"
then you can just use m.scaleOrn(Size);
just like on this screen: