Currently system correctly calculating as you controlled if the qty more than 12 then it should go to semi Bulk location.In semi bulk location you picked 1250 qty and for remaining 10 it will go to fast tract only as it is below 12 qty to pick.
If you do not want that create another location give the range if any thing falls between this qty pick for this location.Create a location to pick the qty requirement (1-100) if any remaining qty falls below pick this location else pick from bulk location.
I am not that much expert but just check this option.