Approaching the border of the first order transition and second order transition is significant to optimize the giant magnetocaloric materials performance. The influence of vanadium substitution in the Mn_1.2-xV_xFe_0.75P_0.5Si_0.5 alloys is investigated for annealing temperatures of 1323, 1373 and 1423 K. By tuning both the annealing temperature and the V substitution simultaneously, the magnetocaloric effect can be enhanced without enlarging the thermal hysteresis near the border of the first to second order transition. Neutron diffraction measurements reveal the changes of site occupation and interatomic distances caused by varying the annealing temperature and V substitution. The properties of the alloy with x = 0.02 annealed at 1323 K is comparable to those found for the MnFe_0.95P_0.595Si_0.33B_0.075 alloy, illustrating that Mn_1.2-xV_xFe_0.75P_0.5Si_0.5 alloys are excellent materials for magnetic heat-pumping near room temperature.