The actual resolution of a Rodinal-developed image will be _worse_ than, say, D-76 1:1 although the print may well appear to be much sharper to the eye.(posted 8639 days ago)Or to put it differently, the Rodinal image will appear sharper while the D-76 (or most any other "standard" developer) image will actually show somewhat finer detail.
In trying Rodinal with HP5+, you might try adding up to 25g sodium sulfite (half a plastic film can) per liter of working solution; that can help reduce the graininess a little and increase the EI by 1/3 to 2/3 stop.