Sounds like you're saying the wind loading code (ASCE 7-10) and whatever you changed it to the second time around are the real culprit? Because you're saying Caesar did what you expected when you changed codes.

I could be wrong but I don't think ASCE has any factor for multiplying the basic wind speed with changes in height. Maybe the second code you chose does change with elevation?

I would've thought the anchor forces would be different regardless due to extra leverage as the pipe got taller and more surface area for the force to apply pressure.