As you have found, a tall
As you have found, a tall narrow kiln with multiple shelves will have relatively significant temperature differences throughout. That’s why some of your pieces are “pointy” and others are more fully fused.
Fusible glass is specially manufactured so that the colors remain true at fusing temps (some shift intentionally, or shift at higher temps) and so that the chance of devitrification is minimized. When you are fusing with float glass, you’ll run into these issues.
Fusible glass is manufactured by Bullseye (COE90), Spectrum (COE96) and Uroboros (COE 90 & 96). (there are a few other manufacturers, but these are the main ones). The glass is more expensive, but it’s also a lot more predictable/controllable.
Jester’s Baubles Fused Glass Designs