I'm not sure just what values are intended but I think the rationale behind them is to :
1) Raise the fan RPM to incease the rain/sleet defelection cabilities of the spinner shape and the fan blade roots. so as to spit most of the stuff out the fan discharge
2) Raise the operating line so that it will make it less likley that the N2 will roll off while processing the rain/hail for the burner
3) should the combinations above not work (for the level of threat encountered) the igntion may recover the engines before they spool down too far
You really don't want to let some aircraft black box spool the engines down while they are eating their full of rain/sleet. At the same time you don't want to be commanding bodie accel/decels that might squeeze you against a depressed surge line while in rain/sleet.