Yeast Cakes: 1 smooth, 1 lumpy - why?

As a water chemistry experiment, I brewed 2 batches of a London Pride clone using the same grain bill, hops and yeast. They were fermented side by side under my stairs which is a steady 68F.

After I racked both batches this weekend, I noticed a big difference in the yeast cake and the krausen level in the fermentors. (see images attached). Anyone know which, if any, of the following could have caused this:

1. Smooth Yeast Cake:
40% water from my faucet and 60% distilled water.
Faucet water is v hard (220 ppm as CACO3) and high in Alkalinity (200 ppm as CaCO3).
Fly sparge
4g gypsum (1tsp)

2. Lumpy Yeast Cake
100% water from the faucet
Batch sparge
8g gypsum

Both appear the same, although 2 has a slightly higher alcohol content (5.4 vs 4.7 abv)
Taste: 1 is a lot smoother and maltier. 2 tastes good, but has a slight harsh bitterness to it (too much gypsum?)

Both will be drunk this July 4th, I dont doubt that, but any ideas on what causes the yeast cake to be so different?

Thanks

Was it a ten gallon boil that was split or did u do two 5-gallon batches? ive noticed my cake seems a bit "lumpy" now that I get a great hot/cold break when i use my immersion chiller. Not sure just how much difference that would make in the final product though, if u chilled one faster then the other...

2 separate 5 gallon batches, one after the other. Not sure which is right/better or what it means, if anything. Both chilled with immersion chiller. Thinking about it now, I know i used a hop bag on the smooth cake batch...i cant remember about the other. As i plan to brew this recipe a few times more, i will take better notes as my memory is fading.