While higher ad position does mean higher CTR, Google will normalize ad position in an effort to compensate. CTR is normalized so ads in top positions which usually have a high CTR don’t have an unfair advantage. While higher positions tend to have a higher CTR, Google expect higher positions to have a higher CTR. For example, Google knows that when an ad appears in position 4 it has an x% CTR. When that same ad moves up to position 1, with no other change, that same ad has a CTR of x+y% CTR. When Google calculates quality score, they remove the impact of the y variable so that they just have the intrinsic CTR of the ad, independent of position. Therefore, while increasing bid may increase CTR, that increase alone should not improve the advertiser’s quality score.