If you go back to any M25 sliders when the slider "gurus" were testing penalty sliders, IG to the left (lower) created the desired affect of the QB throwing the ball away more. Anyone saying to the right side, just isn't correct.
If you think about it, as long as the slider isn't a "placebo" as you say, the lower the IG, the more the QB cares less for getting penalized (even though it is never called) for intentional grounding, so going up on that slider would have the opposite affect, as it should be called more, resulting in the QB not taking a chance of a ball being thrown for intentional grounding. That is if the IG slider actually does affect the QB throwing the ball away more, and after playing M25 for a long time with IG at 1, I did find that the QB got rid of the ball more often, but it really didn't solve the problem of too many sacks on the CPU QB as he would still slide right into a sack by the LDE all the time.
Though I definitely do remember the QB throwing the ball away more in M25. In M15 I haven't seen the QB do that sliding to the right side of the line under pressure, but the CPU does hold the ball too long.
By the way, the penalty settings are FUBAR. They shouldn't affect gameplay like they do at all, but it's been that way for a while now.. and no different this year it seems, sadly.