I read that t*inj delays injector firing for increasing amount of eccentric shaft rotation as rpm rises.. what's the sense behind that?

 

That map alters the injector timing. Injecting fuel at a different engine angle (different part of the "stroke"). So that you can optimise the injection event for the most efficient operation. Normally this means not injecting into an intake event, but injecting before an intake event to set up a fuel cloud in the port runner.