Fig.29.2 Schematic of wall pressure distribution due to viscous interaction [1]  

Region of weak interaction lies much downstream of the leading edge of the plate where boundary layer thickness in sufficient large and rate of growth of boundary layer thickness is very low. The strength of the shock generated due to the presence of decelerated fluid in the boundary layer is also low in this region. As a result of this interaction between outer inviscid flow and the boundary layer fluid is much less in this region due to which pressure on the wall approaches the inviscid flow value.