[Anotheroneagain]

I thought of combining the two:

1 bit per square (empty/non empty) 64 bit.

Then we need at worst 5 bits (32 non empty squares or less) per piece to indicate the positions of the big pieces. (80 bits, typical worst case)

Then we only need 1 bit per pawn, to indicate color. (16 bit at most)

The typical worst case: 160 bits.