D+ and D- voltages for iphone 4 charging

[ozrocket]

This is a general question, not specific to the Minty Boost (as I know it is limited to 600mA).....

Given that setting D- at 2.8V and D+ at 2.0V allows an iphone to draw up to 1A (providing the USB 5V supply can provide 1A safely), and that setting D- at 2.0V and D+ at 2.0V allows an iphone to draw up to 500mA........are there any other allowable voltages which will provide outputs other than 500mA and 1A?

For example, will setting the D- voltage at say 2.4V (whilst leaving D+ at 2.0V) allow a current draw of 750mA?

[adafruit_support_bill]

Please don't double-post. See response in the other thread.