This paper reports the results of two experiments on the acoustics of French mid vowels in a variety in which close-mid vowels ([e], [ø], [o]) occur in open syllables and open-mid vowels ([ɛ], [oe], [ɔ]) in closed syllables, according to the loi de position. Open-mid allophones have consistently higher F1 realizations and more central F2 realizations than their close-mid counterparts, but are not consistently shorter. These results are problematic for accounts of the loi de position as a pattern of vowel reduction, with mid-vowel lowering and centralizing being caused by shortening. F1 and F2 distances between close-mid and open-mid allophones vary across different prosodic and consonantal contexts and these variations can be analyzed as resulting from duration-based undershoot. More broadly, the results have implications for the typology of closed-syllable vowel laxing: they suggest that tense and lax realizations cannot generally be derived from the same acoustic target via closed-syllable vowel shortening but have distinct acoustic targets.