Cumaru Deck Board Cupping since installation in 2012

Описание: I was recently asked about any cupping of my deck boards and I had no real answer so I went out this week (June 2016) to see if I did have any cupping.
Keep in mind I did a fair amount of belt sanding of the boards as how they were supplied from Advantage lumber left a LOT to be desired to get it to what I would call a Grade A finish (which Advantage must think it was but in reality, it's not). I never measured the board before I sanded them but I had bought the 5/4 x 6 Cumaru boards and measuring on scrap piece I had also sanded initially in 2012 measures right at 15/16" thick.
The joists on my deck are spaced at 12" or less and at every point they make contact with the Cumaru boards, I have installed the Ipe hidden fasteners with the stainless steel screws driven in on a 45 degree angle and NOT straight down which I believe helps hold the boards down tight. I have also installed the Vycor flexible flashing on top of all of the joists so there is no direct contact of the top of the joist lumber to the underside of the Cumaru decking boards. This one thing may also be limiting how much water the Cumaru may wick up from the board supporting it.
On my edge or perimeter boards, these do have the most amount of cupping which at the worst spot is only a 0.06" center depression (and 0.06" is less than 1/16") across the 5.5" board face BUT it's there. I have to think that this is happening as the boards overhang the structure and there are no fasteners on that edge so it's pretty much hanging off in the breeze and the board can cup uncontrolled. I may try and add screws towards this unattached edge now that I know the holes can be filled with a mixture of the Cumaru sanding dust and 5 minute epoxy to make an invisible spot where the holes were drilled.