Significant positional amplitude variation and rebanking

[spectre6000]

I serviced a movement here recently, and want to get a gut check on my diagnosis. It's an old (50s) movement with quite a few variants. The mainspring needed to be replaced, and I found several specs listed. The variation I have has a higher jewel count than I've seen listed among the variants, but it doesn't strike me as unusual given how many there are. Because of that, I selected the weakest mainspring I saw listed.

Post service with the new mainspring, I'm getting pretty meh amplitude in the directional crown positions, and 320° or so in the directional dial positions with frequent occasional rebanking. If I reduce the mainspring power, I think it'll stop rebanking, but the significantly lower amplitude in the crown positions gives me pause. It's certainly possible to have two things wrong, but I feel like there might be something extra here I'm missing...

For instance, I thought about pulling a Russian maneuver on it and shimming the balance cock a hair to see if I could reduce the dial position amplitudes without affecting the crown position amplitudes, but that doesn't feel right. Looking for insights. Just get a lighter spring, or is the positional variance suggesting something more?