Had a good discussion of this at a seminar a few years ago. Hardness can also be look at as resilience....the ability to not be adversely affected by a correction...and a dog can be hard/resilient and still be handler sensitive. Csabre gets higher and higher the longer you play/work with her....she starts to refuse to out a ball even....she was given one heck of a correction by direction of Roland Siebel....did not phase her, she did out ball after that (for that session LOL)....Dean Calderon pointed out that this was hardness - she did not shut down, stayed in drive, accepted that correction, complied and continued without any negative results.
At the same time, this is a handler sensitive dog who WANTS to please you, wants to work with you....have never needed to use an e-collar on her, and really, minimal corrections ever needed in training.
Your corrections are apparently not phasing him as they are not strong enough to affect him....a hard dog can take a pretty aggressive correction as I saw that day.
Hexe Sch2, Komet & Kougar IPO1, Kira HGH, SG Bengal, Lynx v Wolfstraum ~ Ziberia IPO1 ~ ATB Basha, Kougar & Kyra, Fenja, Sch3s, Cito, Sch2, DangerRH, Csabre & Alice Sch1s ~Kelsey