A heat exchanger has a first plurality of passages extending in a first direction and to receive a first fluid and a second plurality of passages extending in a second direction, and to receive a second fluid, and the first plurality of passages being formed across a cross-sectional face of the heat exchanger, and there being distinct combined flow cross-sectional areas of the first plurality of passages in different locations across the cross-sectional face of the heat exchanger. A gas turbine engine and a method of forming a heat exchanger are also disclosed.