What ist the maximum Voltage for the IDAC Source? Is it AVDD-0.7 => 4.3V

With a 1mA current source, we can measure until 2k RTD. It seems that the voltage is aproximately 2V only. If i had an 4.3V Voltage Source for the IDAC, it should be more than 4k possible.   What we doing wrong?

many thanks