This study examines whether the degree of vowel-to-vowel coarticulation in French (better known as " vowel height harmony " , V2-to-V1 henceforth) varies as a function of position in prosodic domain (i.e. IP initial vs. word-medial) and duration of V1 (i.e. short vs. long). Following the literature on the phonetics-prosody interface, segments at stronger edges are more resistant to coarticulatory effects induced by their neighboring vowel. While previous studies have mainly looked at non-local V-to-V coarticulation across prosodic boundaries/domains (e.g.,V#(C)V), here we look at V2-to-V1 coarticulation within an Intonational Phrase according to whether target V1 is in absolute initial position (#V1C(C)V2, e.g., #essaie [esɛ]/[ɛsɛ]-'try') or not (word-medial, e.g., épaissit [epɛsi]/[epesi]-'thikened'). The analyses are based on 33k words presenting possible V1C(C)V2 harmonic contexts, which were extracted from a corpus of French running speech. V2-to-V1 coarticulation is measured as the lowering of the first formant of the target V1 (/e, ɛ, o, ɔ/) in relation to the height of the V2 trigger /+high/ (i.e. mid-high and high) vs. /-high/ (i.e. mid-low and low). Results show an effect of prosodic position (but no effect of V1 duration) on V2-to-V1 coarticulation: V1 is more resistant to coarticulation when initial in an IP.