[en] We investigated laser-driven ion acceleration with tightly focused femtosecond laser pulses at an intensity of 5x10¹⁹ W/cm². Targets consisting of thin metal foils either back-coated with a μm-thick dielectric layer or uncoated have been used. The observations we report show that proton bunches with energy in the MeV range have been produced. Furthermore, the protons emitted from back-coated targets exhibit a spatial cross-section which is remarkably more uniform and of significantly smaller size if compared with that of the protons emitted from uncoated foils. The experimental results are discussed in terms of the differences between the propagation of the fast electron current inside the back-coated and uncoated targets.