Because they are the correct values.
The injector offsets that I use for every LSJ I've tuned, are pretty much the same as every LS1 and 3800 I've tuned. I've never encountered this magical 50% offset.
And it's always been the same routine; swap injectors, load new values, make two passes down the road and make minor clean ups. Simple. I just can't figure out why people have so much trouble with injectors swaps.