I'll give it a go, I've been rejoining into one 500'ish coin input after each stake so ive only got to wait for a few stakes till it splits itself to 4 inputs of around 125.
still cant see how 550 can get 3 blocks a day though cause it'd have 4/5 inputs of around 100-125 that take 32hours to mature
Is there a threshhold built in to stop the inputs splitting any lower than 100?
No, it cant be 3 blocks per day with 550 coins on stable basis, more like, with current staking estimates, 2500 lux will give stake per day, 550 coins is about stake per every 4-5 days. More or less.
Afaik, wallet won't split anything lower than 100 coins, it do split everything above 200 coins, mean by automatically, wallet splits all coins with every stake in half, till only remain "optimized" 100+ coin chunks . Or instead you can optimize it manually by splitting into 100-150 coin chunks.