I had no idea how difficult it would be to shape a beard with a straight razor! Clean shaving fine, but shaping....I now have a beautiful line of blood running down my neck.
Sorry brother, I smile whenever people tell me shaving around a beard is easy, I tell them "Try it" The angles are all wrong, the stroke is all off, and you are literally placing one of the sharpest pieces of steel known against your face and then starting a stroke.. Here is what I have learned over that last 31 years of doing exactly this... SHARP, the razor has to be stupid sharp, I have also found that for me I target the 5/8 -6/8 Extreme Hollow, Spike points mostly either German or American... A Japanese Kamisori is also a good option, but it requires a new learning curve with Shaving and Honing... remember the angles and often that kind of scooping action that many use under the nose comes in handy under the jawline
I wish I just shaved it along the jawline, I instead decided to keep most of the hair on the neck and just have it not so far down my neck, which is where I got the biggest cut. I struggle with my neck anyway but I was surprised how difficult it was simply getting a neat line across the middle of my neck. I should probably learn the direction my hair grows. I also had difficulty shaping the cheek area, to get a good sideburn shape. I initially just wanted to grow a beard but I've become an addict to traditional wet shaving and just had to find a way of shaving my face while still keeping the beard.
I would reeeally suggest one of the vintage SEs for this. An Autostrop Vb-1/2 or a Wilkinson Sword Empire have been best for me to use and maintain my 'stache lines. I use everything, but DEs and most of my straights leave shading on the sides, or remove desired growth, if I'm not careful.