We worked with Jason via our email ticketing system on this issue. Posting the relevant details below for the benefit of others searching for similar solutions.
From what I’m seeing on Dell’s site, the 2310H supports DVI and VGA along with DisplayPort:
“Flexible Connectivity: Analog (VGA) and digital (DVI/HDCP) cables both come standard. Add an optional DisplayPort cable for excellent digital connectivity.”
If this is the case, then DVI from the dock to DVI from the monitor is the best approach.
If the spec page is wrong and the monitor only has DisplayPort, unfortunately there aren’t really any options for making our dock work. As you mention, DisplayPort (source) -> HDMI (display) generally works (because DisplayPort outputs carry an embedded HDMI signal - a neat engineering decision), but HDMI (source) -> DP (display) does not work.
So if it only has DP input, the only option will be to return our dock and purchase a model which has DisplayPort output. (I believe Dell makes one.)
Hope the above helps, and let me know if any other questions.