Fe-Al alloys strengthened by coherent phases are designed for high-temperature (HT) applications in thermal power plants. Lattice misfit (LM) between phases plays an important role in the microstructure and HT performance of structural materials (e.g. creep resistance). Hence, LM can give guidance for the development of new HT alloys, but only with proper micromechanical understanding of the interaction between matrix and precipitates at operation temperatures. We found that small Ti addition in ferritic Fe-Al-V alloys strengthened by L21 precipitates can produce similar alloys but with negative, null or positive LM. Hence, we propose to perform Neutron diffraction in-situ tensile tests, at 873K and with loads up 800MPa, to answer the question: What value and sign of LM are optimal to increase the load transfer from the matrix to the precipitate at HT on L21-strengthened ferritic alloys?