with the straight, it was easy due to the back to get an correct angle, but maybe it's like you say, that angle that way is not good.
It's not that the angle isn't "good." It's that unless you use a specific sharpening rock like a coticule, it's not really sharpening the very edge of the razor. It's too acute to do that.
IME, and there are a whole lot of people who will disagree, hardened steel can hold an apex angle of approximately.... 55 degrees. That's the best a good steel can do, if you look REALLY close at the apex. The apex of a well sharpened axe or a straight razor or a microtome blade are all approximately the same, when you look close enough. The axe will shave fine. It might leave an angled "stump" at the base of the hairs, if you really nitpick, because the thickness of the metal behind the apex starts to wedge in the hair and bend it. But in an hour, you won't be able to tell the difference, anyway.
Now when you lap anything, you will not get exact, crispy corners. The leading and trailing edges will get rounded off, period. The rougher/larger the grit, the more rounded the edge is going to be. The more uneven the stone, the more rounded the edge will get. The more loose grit on the surface of the stone, the more rounded the edge will get. So depending on the stone you use, you might get a really good edge even though you're holding an angle of 15 dps per side, forming only a very faint bur, which leaves a great edge with just a couple swipes on a strop (or pulling the burr off with a piece of wood). This is because the stone is rounding the edge just right for what you want to end up with. For this particular tool and steel, anyhow.
The way you sharpen a straight razor, it's like "sharp edge for dummies." You are thinning the edge bevel super thin, but you're usually just thinning the metal behind what is eventually going to be the edge. Then you can't hardly miss to get a good edge on what you have made. If you use a coticule, you might get a perfect edge right off the bat. It just happens to have the grittiness and particle size that can apex a razor, automatically, while honing on the spine. If you use a super hard and fine ceramic which barely rounds the edge, and you just strop lightly a few times, you can get what passes for a well formed apex, but it will fold and crumble away after cutting a few hairs. It's too thin. But if you strop it some more, bang, you get a great edge.* If you use a really rough stone with loose grit, you will over round the edge. But a couple swipes on a fine stone (at higher angle; lifting the spine off the stone), and bang, you have a great edge. Because it's still thin enough to do the biz.
*In lieu of stropping, I will usually just wipe the apex on a smooth bit of ceramic at approximately 25-35ish dps, with barely any pressure, only until the burr is completely gone. This will give an excellent shave and a durable edge. A strop might make it a little better, but at this point it's hard to tell. This 30ish dps is about the same "burr removal" angle I would use on a knife, axe, str8. It doesn't matter. Cuz.... steel can't hold an edge much finer than that, IMO. Of course, this is with a fine, fine ceramic. As said, the rougher muddier the stone, the more it rounds the edge, so finishing on a rougher stone, the finishing angle will be less. But there are probably 100 million people who think this is plain wrong.
If you don't like scratches and you want an "automatically" sharp edge, by doing same motion over and over again like a robot through a progression of stones, it's hard to mess up with waterstones plus or minus a strop. If you learn to sharpen on dimensionally stable stones, you can maintain and tweak and modify an edge is no time with just a sliver of rock.
I suppose if you looked CLOSE enough, the apex on a knife is pretty much indefinable... just jagged bits and whatnot. To clarify, using the finest and most dimensionally accurate common abrasives (like fine ceramic), the finest angle you can get is somewhere north of 50 degrees. On some steels maybe north of 60. There are finer grits in emulsions/strops and films, but even the plastic 3M films have "give" to them which round the edge, like a strop.