WTf seriously, size mods work everywhere and anytime unless the GM's have screwed up something o_O
Do you people even know how size modifiers work? ._.
Size modifier affects weapon ATK only!
It doesn't decrease your overall damage.
So when using a +10 DDTP main gauche, you'd normally have 63 weapon ATK, when hitting a medium sized target it drops to about 47. So you only lose about 16 ATK.
+7 Ice pick only loses about 33 ATK.
etc etc.