Who's the toughest pitcher to HR off of?

In the past I've compared & ranked pitchers based on W's, ERA, K's/9IP, and BB/9IP, but there's another stat that tells how tough a pitcher is: Innings Pitched/HR allowed (IP/HRA). The top 5 starters so far this season are:

1. Tim Hudson (ATL) - 37.92 IP/HRA
2. Jake Peavy (SD) - 34.50 IP/HRA
3. Brad Penny (LAD) - 34.00 IP/HRA
4. Chris Young (SD) - 29.67 IP/HRA
5. Chien-Ming Wang (NYY) - 21.61 IP/HRA

I don't know what the heck this has to do with the hobby, since runs can be scored in a lot of other ways, but just thought it was kind of interesting to see (especially in this day & age of so many big HR hitters). Of course those other stats mentioned above are much more key in driving the value of a pitcher's cards.