Using ellipsometry we investigate the influence of a gradual change in the amphiphilicity of short-chain oligo-ethyleneglycol monoalkyl ethers (CnEm) on critical adsorption and incipient wetting of an inert liquid perfluoroalkane (F) substrate by the aqueous amphiphile phase (AW) near its upper miscibility gap. For the shortest molecule, i-C4E1, a pronounced increase of the adsorption of the amphiphile is observed as the phase separation temperature TB is approached at concentrations w below the critical composition w(c), indicating incipient wetting of the W/F interface by the amphiphile-rich phase A. For the longer-chain molecules C5E2 and C6E3, an opposite behavior, viz., increasing adsorption of water, is found for T --> T-B for concentrated mixtures (w greater than or equal to w(c)), indicating incipient wetting of the A/F interface by the water-rich phase W. This crossover from preferential adsorption to depletion is attributed to an autophobic effect of the oriented monolayer of the longer-chain CnEm molecules, which is expected to be absent for short-chain molecules with a globular tail like i-C4E1. The depletion effect also disappears when perfluoroheptane is replaced with octane as the substrate phase. We discuss these results in terms of critical adsorption and incipient wetting effects and provide complementary information from interfacial tension measurements.