IME, absorptive and/or diffusing treatments at the first reflection points can help with high frequency problems. As you go lower in frequency, these devices become less effective. Below 100hz or so, Hemholtz resonators are the only reliable treatments that I've found (other than room correcting EQ schemes).
It's hard to say whether 1" foam will work for high frequency issues until you try that foam in that room. OTOH, it's easy to say that you'd be very unlikely to get any benefits from 1" foam at low frequencies.
It's hard to say whether 1" foam will work for high frequency issues until you try that foam in that room. OTOH, it's easy to say that you'd be very unlikely to get any benefits from 1" foam at low frequencies.