OK, it looks like the info here went sideways pretty hard...
Before adjusting injection timing, it's important to understand why it's there. Most OEM applications are timed to inject fuel against a closed intake valve. This does two things; it cools the valve and aids in evaporation. When the engine is cold, fuel takes longer to evaporate, so it must be injected sooner to get enough of the liquid evaporated to enable clean combustion.
Clean combustion is the key here. If you're burning everything you injected and you had decen charge mixing, it shouldn't matter as much when you injected it. On the other hand, if you're either not burning liquid fuel in the chamber or not mixing completely, it can skew what you think got injected into the cylinder. This is why the OE calibration injects earlier on a cold engine to allow time for fuel to evaporate and mix prior to combustion. (Look at the table and you'll see the trend!)
In the aftermarket, we have the nasty habit of plugging huge cams into engines that open the door for a couple problems. One is that the lower port velocity reduces charge mixing at low engine speeds. The other is that having both valve open simultaneously (during overlap) opens the door for "short circuiting" where vaporized fuel may escape out the exhaust valve without ever being burned if there isn't sufficient port velocity to push it down into the cylinder. This can usually be addressed by delaying the injection event slightly so that the vapor isn't there when the exhaust valve is open. The potential downside is that large quantities of liquid fuel being injected into a cylinder at low port velocity may lead to bore wash at extended idle.
If you see a change in AFR resulting from injection timing, it just means that you didn't get a complete burn in one case. The object is to completely evaporate and burn whatever fuel you inject, regardless of what's going on with the aircharge or port velocity. This was one of the exercises we did in my last advanced GM tuning class with a 23x+ camshaft in a GTO. Once you find clean combustion, it's a lot easier to dial in the VE (or VVE) tables, THEN you can address idle airflow targets.