Well I always assumed each time Bruce turns i to Hulk he starts out at a certain strength level. As he gets angrier it begins creeping up. Now I'd assume they measured the time his strength increase based on level of anger and made a Plan based on that.
As long as when Hulk is rampaging they defeat him within a certain time limit before his strength rises too high for battle, they should be fine and thus they made Hulkbuster a couple of tons(strength is commonly measured in tons with the superhumans of the MCU)stronger than the Hulk so he'd be able to outmatch and take down the Goliath the moment he gets outta hand. Of course that's just my thoughts, I could and most likely am FAAAAAAR OFF.