Import pressure using linear interpolation

Hello everyone, I'm doing a analysis to find the displacement and stress on a wing under the pressure field. And I imported the pressure field using linear interpolation with the data export from Ansys. And I have encountered a problem, the pressure field supposed to act in the outer surface of the wing skin. But instead only a part of the pressure is acting in the outer surface,other part acting in the inner surface of the wing. Could anyone tell me, why is that happening? And how can I correct it? 

I would be very grateful to receive your answers. Please help me out! 

Thank you so much!

P/s: I have uploaded here, the picture of my problem, the .hm file, and the pressure file, if you need to see it. 

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