This is because you have hardcoded your script to use 3 signatures. When the Leakage bits decreases below 128 you might need more and more signatures as you move up.

Check here https://github.com/iceland2k14/rsz/blob/main/LLL_nonce_leakage.py
for the generalized Matrix form reduction and also the function Minimum_Signature_Required for each Leakage bits.