I can think of a couple of different possibilities. One is simply that you have become used to not hearing the lower frequencies, due to your somewhat less common hearing loss. This will just take some time to get used to. Does the static noise seem like high or low frequency?
If it is higher frequency another possibility is that the relative gain at the high frequencies is too much. There are different fitting formulas that can be used to prescribe the gain vs the frequency. Phonak probably have their own proprietary one, and there are a couple of other industry standard ones used like DSL v5, and NAL-NL2. The latter still provides some gain at higher frequencies where you hear well, while the DSL v5 provides no gain at higher frequencies. My hearing loss is very different from yours, but I would think the DSL v5 would sound a lot softer than NAL-NL2.
Not sure about the KS9 Phonak aids, but some can use different programs in the aids to use the different formulas. For example you could ask the fitter to put the Phonak prescription in one, the NAL-NL2 in another, and the DSL v5 in a third. Then you could compare each over an extended time to see which one you like. They are all valid formulas, and it comes down to what you like to hear, and how well you can hear speech if that is your main concern. If the aids cannot handle multiple programs with different formulas then you would have to have each one put in at the office and try each to see what you like. Here is what a DSL v5 prescription would look like for your loss. Note that it gives more gain at low frequencies and none at high frequencies.