I have read that for front vowels, the cavity behind the lips (I think this must correspond to the space between the lips and the hump of the tongue) is F3, whereas for back vowels it is F2.
In that case, what dictates F3 for back vowels? Is it the space between the hump of the tongue and the pharanx, with the space between the hump of the tongue and the lips becoming F2 (because it is the smallest of the three spaces in this configuration)?
What does F4 correspond to, and does this vary depending on whether the vowel is front or back? Is there a fourth resonator / airspace somewhere?
Would a vowel with formants 335, 1515, 2680, 3350 Hz be considered a front vowel or a back vowel? By the criteria I have found it is between the two - so I am not sure what F2 - F4 represent. Specifically, in a vowel with approximately those formants, how can F3 be raised without also raising F2 (or how can F2 and F3 be pushed apart)?