AD8231 output offset and voltage drop issue.

Dear Sir:

               I used AD8231 in our circuit as below picture (For +VS=5.06V supply, with nCS, A0, A1, A2,-VS to GND) , We have some issue when we test AD8231 as below:

1. We tried to short +INA and -INA , the outputA have 2.9mV offset , then I check parameter from AD8231 datasheet , Voso only 30uV , Is it normal?

2.We tried to used differently DC for test conditions then OUTA still  has 20mV voltage drop.

     Input INA+=30.0mV (DC)with INA-=GND, the OUTA=9.7mV (~20mV drop)

     Input INA+=100.1mV (DC)with INA-=GND, the OUTA=79.0mV (~21mV drop)

     Input INA+=200.0mV (DC)with INA-=GND, the OUTA=179.1mV (~21mV drop)


Is it normal?