Have you tried at 71+?

ShB crafts are a little bit of a hurdle at 70. Meaning being below the recipe level, you have a big penalty to synth and quality increases. I'm not sure the exact reason, but this is far more pronounced at lv70 trying to craft anything 71+ than it would be at (example) 72 crafting a 74 recipe. Even Ingenuity doesn't cancel this out.

I can't say for definite this affects quick synthing, but it's likely.