We add Grunty's opinon on Buns (-1) + Buns opinion on Grunty (-5), multiply by 2 and then alter effectivity by it (100% - 12% = 88%). Thus cth received by spotting is lower than it would be for totally bland mercs. Sexism/racism don't factor in, because Grunty is non-prejudiced and too average for Buns to care.

While this calculation is correct, I am very surprised that both have a negative opinion of each other. But this data seems pretty vanilla to me, no changes since the file is under svn... dafuq?

This really irks me. Either merc opinions were always somewhat borked, or they've been messed with a long time ago.

Edit: Wait a minute. Ignore the last part. Damn, this game is ingenious :professor:

What I said above is true at the beginning of the game. Grunty learns to like Buns in an ongoing campaign. Which increases his opinion up to 25. Then, the modifier becomes 25 + -5 = 20, which then becomes a 2*20% = 40% bonus on cth.

So if the base cth gain were 10%, she'll get 8% in the beginning, but 14% later on.