Why not good?
And why would it be good with the shittiest technique and dilution possible (stand), but not good with double the concentrate?
Some of my best HP5 work has been developed with rodinal... so all I can say is that it works quite well.
You are either very lucky or easily pleased, even Ilford don't recommend HP5+ in rodinal, unless you over develop by a long way you can't get great negatives on HP5 with Rodinal, or, I never have been able to, in most other developers yes, but it doesn't seem to suit HP5, this from a very long term user of Rodinal, I have used HP5+ along side other films, but admit not for many years, since I found Fomapan,, although pretty much every other film I have used produces terrific negatives with Rodinal, HP5+ although a great film, always produced very thin negatives, lacking detail, just one of those things, unless, of course, Ilford has changed the film in the last few years without telling anyone