A lot will argue back and forth, this is where a dyno comes in handy.
But you are on the right track, some like to say that they achieve 19-21* of timing but don't include what you just said, that after 5500 rpms or so it starts to drop again, or it's not steady at all like it shouldn't be.
You want it to gradually increase with RPM, but if you are seeing or feeling better results doing it like you described, then try a higher pulley to see if it is a big difference. Either that or look at other points in your tune at that rpm, may need more fuel?
