Get a bigger intake, there's no need for this much negative pressure, I see it all the time though, it only needs to be sufficient so smells don't escape, when your tent is sucked in this much you're greatly reducing the ability of your equipment to control your environment, I bet if you had a bigger intake you would even be able to turn your exhaust down abit and still maintain the same environment.
I do understand why people do this cos it's scary to think smells might escape but it really isn't necessary, ANY level of negative pressure will do the trick
hope this helps