DC-Coupled AD8310


I want to use the AD8310 with a DC-coupled  input. I am using the setup from the datasheet in Figure 38 (page 19)  reproduced here:

However, I have an extremely poor dynamic range. The   dynamic range of this circuit is advertised through Figure 39 (page 19)   of the datasheet, which is reproduced below:

I  am not getting this dynamic range no matter what I adjust the   potentiometer to. The lower end of the range is limited at an input of   about -30 dBm.

Any ideas how I could troubleshoot this?

If it helps, if I use the basic AC-coupled configuration (show below), I DO indeed achieve the advertised dynamic range.

Thank you for your time!