Allow me to educate you.
Fire-resistance does not give you somekind of % damage cut on every attack. It does not infact really add up. Resisting magic damage causes the target to take 1/2, 1/4, 1/8, or 1/16 of normal damage. That is all it does. There is no multiplier going the other way. And to actually resist with any type of consistancy you need to be wearing 100+ in resist gear. To resist 90-95% of the attacks you need to wear about 160 resist or more. What you are gonna resist in your typical fafhogg tank equip is about possibly 1 breath. And thats so random you probably would resist that one even with the BQ ring on.
Dont confuse reduction from positioning with an actual resist.
To further prove my point, i can also tell you that just because your screen may show -75 fire-resist, it doesnt mean your actuall fire-resist is -75. The screen shows a sumarize of your gears added resistance. Nothing more, nothing less. You actually have a base resistance to any element. Base at 75 is about 225, with BQ ring thats about 150. You see, even if negative resistance DID add damage, i dont actually think there is any way to actually achieve it.
Do i need to go on?