If you use
PHP Code:
setshape(1, widthinpixels, heightinpixels);
//for instance: this.setshape(1, 48, 48);
this will set the blocking shape size of the NPC, then you could for instance re-adjust any ganis for the shape to be centred.
Unfortunately using showcharacter(); enforces a blocking shape of 32 x 32 pixels offset by 0.5 x and 1 y (same as players).