I guess you are referring to the Importance sampling, anyway the shadow sharpness depends from the quality of the HDRI.
If the dynamics is poor, the shadow are weak. You can adjust the brightness of the sun in PS for having more exposition range and, as a consequence, sharper shadows
Sorry, I was on a phone when posted this and tried to make shortcuts XD. My apologies.
Shadows work for objects when the shadows clash with other objects, so my HDRi's are fine. I have been using these same HDRi's for awhile now.
What I meant was, in older versions of octane there was a floor shadow that was projected from the object when using HDRi's. I didn't have another object there to catch the shadows, like a plain object or other types of geometry. This was back in the Octane 1.0 days or something like that. However, now, in the latest build, it seems like I need to have geometry under my object in order to catch shadows. So, I guess you can say it was a fake shadow.
I'll upload an image that I rendered with an HDRi in octane awhile ago, to kind of show what I am talking about.
The only object in that render is the vehicle, the nthe HDRi for lighting.
2x Titan Z
1 Geforce 710 (For Displaying to the monitor)
AMD 8350 CPU
(Will be using the most up to date versions available. Always)
Octane Plugin for C4D R15
Octane Plugin for Houdini 15https://www.pwndesign.com/