The picture shows that with more projection the hook angle is smaller. IIRC I drew a 5" diameter head with a 1/8" projection at 45° hook angle for the initial picture. Then I extended the knife 1", to 1-1/8" and the hook angle changed to 34.58°.
From an efficiency standpoint you want the hook angle to be as large as possible. Think of hand carving with a knife; you want the blade as close to parallel to the wood as possible. Imagine how difficult it would be if you held the blade perpendicular to the surface.
The principle is the same for rotary cutters such as a planer. The problem the comes in is that hardwoods tend to chip if the hook angle is too great, so you have to reduce it to the point that it diminishes enough to satisfy your needs. As in the example with the hand carving, decreasing hook angle increases the force necessary to make the cut, and decreases life of the knife, both because of more "scraping" action as well as in increase in heat from the friction.
Practically speaking that means selecting a compromise as you generally can't just choose the hook angle you want, as it's primarily determined by the head. It's easier with shaper/moulder heads since they are designed to be interchangeable, but even still there are generally only a few hook angles available. We have a few with both 12° and 20° pockets and generally use the 12° for hardwoods and 20° for softwoods.
Getting back to your observation about a large projection working better for softwood with your power hand planer, the only thing I can say is that it must be for some reason other than the change in hook angle. I'd be interested to know what is "better" about the cut when planing softwood with the knife further out?
I've never used a power hand planer, so I don't really know, but the only thing I can think is that you need the knife deeper for hardwoods because A) it increases the hook angle which reduces power requirements, and B) the smaller radius also reduces power requirements because of leverage. BUT, it seems like softwoods would also plane better with the knife set further in; however, if there is enough power to plane softwoods with the knives further out, I could see that you may be able to plane more, faster.
I really don't think hook angle has anything to do with the situation you're describing. Yes, it does change, but I don't think it's changing much, and the characteristics you've described so far seem to be the opposite of what changes in hook angle normally produces.