You're doing great, especially with the grinder you have. Angling the blade is about all you can do.
On a 2x72 this is an easy process. There are two ways to terminate the plunge at the top- a straight line, or a little swoopy curve.
If you want a full height grind with the little swoopy curve at the top of the plunge, you track the belt off the side of the platen, let's say 1/4 inch. That way the belt has no support under that last 1/4 inch where it hangs off the side of the platen, and thus where it contacts your plunge line. Because of this your plunge line will be defined most of the way up, but at the top where the belt flexes away from the blade it doesn't cut as deep. The belt "falls off" as a smooth curve as stiffness falls off. How far you run the belt off the side of the platen determines the length/arc of your swoop.
Then when you make passes on the other side of the blade, you track the belt 1/4 inch off that side. Repeat this process each time you switch sides on the knife.
The trick is then learning to track the belt off the side evenly when you do each side or else your little swoop at the top won't be the same on both sides. This is where a file guide is worth its weight in gold because you can sneak that file guide right up to the edge of the belt and you know you're creating the same angle on each side with no fear of the belt jumping out of the plunge and eating your plunge line up.
For straight terminations, you do exactly what you do on your current grinder and you mark a line along the top of the blade where you want to terminate the bevel, and simply stop grinding when you get to that point to make sure you don't break through the spine with the plunge. Layout fluid and a caliper works great for this.
By angling the blade, as you did above, you can draw your plunge lines out but you still have to decide how they terminate, straight or swoopy.
***With the grinder you have, hand sanding will be your best friend. You can do a whole lot to the terminations on your plunges based on how you hand sand. Stop your plunge about an 1/8 inch below the spine. If you want to soften a hard stop into a swoop, hand sand with a piece of leather between your sanding stick and the sandpaper. Sand the top of the plunge and the spine area until the plunge fades at that corner. Don't overdo it because you don't want a rounded out divot there. You're only looking to soften the corner and blend it some.