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I decided to terminate the Falcon-Chess match (I had let it run so long only because I was away anyway) after 676 games, at a score 356-320 (53%). Although this seems only a small difference, this is always to be expected in symmetric playtesting: they start out with equal material, and not all games will have R for F trades. And even for those that have: when I ran games that were imbalanced from the outset (RR vs FF), I never saw more extreme scores than 57% (and for only a single R-F imbalance, that would be halved).

Nevertheless, over this many games, a result of 53% is significantly
different from equality. One side scored 36 more wins than the other. The
standard deviation of the number of wins in 676 games is about 24. So the
deviation translates to 1.49 standard deviations, which has only a 6.7%
probability of occurring if the two engines were equal.

So the conclusion must be that it is almost certain (more than 93%
confidence) that it is better to value Falcons slightly lower than Rooks
than to value them above Rooks (in a simple scheme that has fixed piece
values throughout the game, like Fairy-Max). Current Fairy-Max has R=475, so I set F=450. (B=350, P=100.)

I have not had time to watch many of the games. (I will study the PGN
later.) Usually Fairy-Max is very materialistic: it has very little
positional evaluation, and the diffence between having a Knight on a1 and
on e4 is only about a quarter Pawn. If it lets undefended Pawns live, it
is usually because they are heavily poisoned.