Setting the reinforcement counter before the battle doesn't exactly set the exact number of reinforcement points, it only changes the precent. For example say a map normally has 100 reinforcement points, then keeping the setting at "100" gives you 100 points, changing it to "80" would give you eighty points and so on.
However all maps default scores arn't the same, some might be default 150 for example. So setting the counter to "90" gives you ninty percent of 150, instead of the exact number 90.
Not being paranoid doesn't mean someone isn't trying to kill you... or does it?