The only parameters that should affect the impedance calculations are trace width, distance between traces and stackup.
Considering that the trace widths and separation is not somehow altered during the import, we should start with making sure that the stack up was imported correctly.
step two would be to make sure that in setup- > options -> general settings the tool is set to include the ER and loss tangents for metals and check for the default values since if the stack up did not come through ok, HLDRC will assume these values.
If none of these work, it would be a good idea to look at the layout tool to make sure that the impedance value of 82 ohms is correctly derived.
Thanks Kanchan for your comprehensive response.
The import was OK but I needed to adjust my stackup and remove resin flow compensation to get your impedance results.