What you are changing that makes a handling difference is the rear roll center height. Back in my Z-16 days, that was my main tuning tool. For dry conditions, we'd keep raising the rear until I started to get wheelspin, and then back off 1/2 turn on the rear perches. That method was never wrong for that car. In the wet we'd run it as low as we could w/o scraping the ground in the rear.
Why your front weights would change much raising the rear 1/4" is not apparent to me. The calculations of how much the CG moves and affects front-rear weight distribution don't support that.