I think the key word is "potential" HP per cfm of intake flow. As Werby mentioned, you need a race motor calibration to really take advantage of that.
I usually use a factor of 2.1 HP per cfm if I'm building a real strong engine. Here's a few examples from some of the engines I've done over the years:
511" Medium Riser used at Drag Week 2005, peak intake flow was 340 cfm at .700", HP was 706 at 6700, HP per cfm was 2.076
530" High Riser used at Drag Week 2013, peak intake flow was 401 at 0.800", HP was 850 at 7100, HP per cfm was 2.119
585" SOHC used at Drag Week 2016, raised and welded intake ports flowed 460 at .700", HP was 1004 at 7100, HP per cfm was 2.182
504" Medium Riser used as a dyno mule for testing the 351 intakes, if I recall correctly peak intake flow was 330 cfm from Joe Craine ported Edelbrock heads (Joe, maybe you can check this?), peak HP was 723 at 6300, HP per cfm was 2.191
None of these engines were really maxed out; for example, none had 15:1 compression, most were 13:1, and the first one on the list was only 11.5:1 if I recall correctly. But I have seen legitimate dyno data of numbers of up to 2.4 HP per cfm, on a really high winding small block at another dyno, so it's possible to get pretty far past 2:1 for HP per cfm. The intake tract is the critical piece...