The back of the tongue (dorsum) and the roof of the mouth both have large surface areas compared to e.g. the lips. In English, dorso-velar plosives can be made at a number of places along the roof of the mouth, and this is especially so for combinations of [k] + vowel.

If you say the words ‘key’, ‘cat’ and ‘court’ (or words with vowels close to CV1, CV4 and CV7 or CV8), and isolate the initial consonant articulation, you should be able to feel that the back of the tongue makes contact with the roof of the mouth in different places. For ‘key’, the articulation is quite far forward (advanced), which can be transcribed with the diacritic . For ‘court’, the articulation is much further back (retracted), and if you compare this [k] sound with that of ‘key’, you will hear that it has a lower-pitched ring to it. This is partly because the lips are rounded (the vocalic articulation includes a high tongue back and lip-rounding); but even if you unround your lips, the sound is still different. The diacritic for this is . The sound in ‘cat’ is ‘neutral’: neither particularly front nor back when compared to the others.

This variability arises because the plosive consonant is co-articulated with vocalic articulations which differ in tongue frontness and backness and in lip posture. Already in hearing the [k] sound in ‘key’, some secondary articulations associated with the vowel are audible. Because they anticipate the next sound, this is often called ‘anticipatory co-articulation’. At a narrower, more detailed phonetic level, then, we have as many ‘kinds of [k]’ as we have kinds of vocalic articulation.

We have talked about ‘vocalic articulation’ and not ‘vowel’. This is because velars do not depend on vowels for their place of articulation: they depend on the subsequent approximant or vowel, whichever is closer. In the word ‘screen’, there is a retracted , not the advanced  of ‘keen’ or ‘ski’. In this case, [k] is co-articulated with [ɹ], which for many speakers of English has a secondary articulation of velarisation and/or lip-rounding. Likewise, in ‘queen’, the velar articulation is co-ordinated with the labiovelarity of [w] and not the frontness and spread lips of [i].

Note that this relationship between vocalic and dorsal articulations is not reciprocal: in sequences of vowel + [k g], the place of articulation of the dorsal is less adapted to the vocalic articulation than in [k g] + vowel: compare ‘keep’ and ‘peak’ and ‘caught’ and ‘talk’; you will probably find that when the velar comes after a vowel, its place of articulation is neither particularly front nor back as compared to when it precedes a vowel.