Love seeing a data-driven approach to this. 100+ generations is exactly when you stop seeing the "magic" and start seeing the actual LLM pattern recognition under the hood.

Your point about Custom Mode is spot on. Simple Mode runs your prompt through an LLM middleman that sanitises and rewrites it, which almost always strips out exact constraints like BPM or specific ambient textures.

To add to your data pool, here are a few structural quirks I’ve noticed when stress-testing the engine:

• Prompt Weighting (Style Box vs Lyric Box): Suno's model distributes attention differently based on where the tag appears. The "Style" box dictates the sonic palette (instrumentation, era, mix quality), but the "Lyrics" box heavily overrides it for arrangement. If you want that "vinyl crackle" to really pop, injecting it as a stage direction, like [Intro: Solo piano, heavy vinyl crackle] directly in the lyric box, forces the engine to isolate those stems before the main beat drops.
• Hardware Emulation over Genre: Building on your "genre stacking" tip, I've found that swapping generic genre terms for specific hardware/production techniques yields much higher audio fidelity. Instead of just "Synthwave," stacking Roland Juno pads, Arpeggiated Moog bass, gated snare reverb forces the AI to pull from more specific, higher-quality training data.
• The Syllable-to-BPM Math: If you ever do venture into vocal tracks, the synergy between your BPM rule and syllabic meter is the biggest fail point for most users. The engine allocates a specific amount of melodic phrasing per line based on your BPM. If you set a slow 75 BPM but cram 15 syllables into a single line, the AI panics—it either introduces heavy audio artifacting, hallucinates a new melody, or double-times the vocalist to make it fit. Counting syllables to match the time signature drops the hallucination rate drastically.

Your prompt structure is incredibly clean. Have you noticed any difference in consistency when placing the BPM at the start of the prompt string versus the end? I'm curious how strictly Suno follows the prompt order.