I'm a little unclear on why you are using a parameter to pull values from the calculated field B. Parameters are not dynamic, so even if the values from B change when filtered, the parameter won't reflect that change.
I'm not completely clear on your data, but it sounds like you can just make an equation for A for those values from B
(i.e. if B>=10 then "Outcome1"
elseif B>30 then "Outcome2"
else C end")
And then only have one parameter changing that percentage.
Otherwise, posting a workbook for us to see what you are talking about specifically would be really helpful.