That is a feature of the patch, and it is a feature of the OP patch.
The reason its there is the game mesures range from the hardpoint on the model to the target to calculate range for to hit and damage calculation. The range is mesured from the hard point to the models center. Unfortunatly when using oversized models in the game this is essentially a cheat, because the larger model has the advantage over a smaller model my being due to the model size somewhat closer in range. The larger the model, the more the problem. It became a fairly easy way of cheating. the file that sets model size is also now checked for accuracy to ensure cheating isn't happening.
If your only playing the game single play, then go ahead and mod the model.siz file (note pad will do, don''t forget to back up a copy of the file, and remove the read only attributr on the file befor editing or you won't be able to save your modded file.)
Moding the file and then playing a multiplayer game is going to tell everyone your playing in a one up fight on Gamespy that you've modified the file. Most d2 servers won't even let you join the server if this file is changed.
Hope this helped you understand whats happening.
Cordially
Terrance "Sandman" Roff
Dynaverse 2 technology tester, Outer beta since 2000