A gas turbine engine component has an airfoil extending from a platform to a tip at an end of the airfoil spaced from the platform. The airfoil has a suction wall and a pressure wall, with at least one channel extending toward the tip from the platform. A plenum communicates with the at least one channel. The plenum flows from the suction wall toward the pressure wall at the tip to communicate with cooling holes near the pressure wall. The plenum has a reduced cross-sectional area between the suction wall and the pressure wall, and an increase in cross-sectional area downstream of the reduced cross-sectional area. A mold core is also disclosed.