it isnt that the porterate mdl is big its that you have it zoomed to far in or dont have a portrait so it picks a portrait randomly when the unit is selected, Heres a tut with war3modeleditor
Step 1 open mdl
step 2 go to windows<sequencemanager
Step 3 rename stand -1 or we animation u wana use, or creat another copy of it, rename it to STAND PORTRAIT
now go to windows camera get your screen to where u want portrait to be, then click creat from current location
then name it PORTRAIT. save and exit