=IF(1/(1+10^((B$13-B6)/400))>=0.92, ".92", 1/(1+10^((B$13-B6)/400)))
The reason you are getting a FALSE result is that you didn't tell Excel what to return if the logical_test of the IF statement is False.
FALSE is the default answer if a value_if_false is not specified.
P.S. You do realize, don't you, that by placing " " around .92 you are telling Excel to return the Text version of .92?
That may impact what will happen if you refer to that cell in another formula.
Certain Excel functions will see the .92 as a number, but others will see it as Text.
If it's truly a number, don't use the " ".
re: "I hope my question isn't too complex to answer
Not even close! ;-)