It doesn't matter what the total of all of the modifiers from Table T-4.6, you subtract it from the Failure roll.
If the total of the modifiers was positive (which is likely to be very rare), then yes, that will make the failure less severe. If the modifier IS positive, treat the multiplier as a divider (i.e. if the results says 2 times the mod, if the mod is positive, make that into "modifier divided by 2").
If the total of the modifiers was negative, that will make the failure roll more severe.
Remember, the wording is based on the concept that the total modifier WILL be a negative, so that means that you have to make adjustments accordingly.