I'm using Wordpress and using multiple Directory rules with the ExpirePeriod and Extensions options, I was able to solve this problem. I'm using "Path = /" to be sure that the whole website is targeted by the rules. And with multiples Directory rules, you can have different ExpirePeriod for the different types of files.
You can build the rules you need with the following template and the speed test should be happy (well, except for the objects not on your server but they fail to understand that I have no control over those kind of thing).
Path = /