It appears the bucks are all completely flat. Is that correct? How about making a tapered buck? Something similar to an upside down V only subtle. Would give you a good slope, slightly more insulation, a bit more wiggle room for window irregularities, and would be more of a "press fit" per say for our window installations. It would also allow us to change window placements based on geographical locations for Solar gain, or even for esthetic and practicality purposes.... etc, etc..... Same concept we use currently when building our own bucks. We can place the window further to the outside, inside, or meet in the middle. Or even a directional taper. Though I prefer the idea of a subtle bi directional taper. Just thinking outloud here. Love the proprietaryness (new word?) of the system already. It looks to be a solid system. Appreciate it y'all!

You could just put insulated glass in your 2x4 window :)

I like the buildblock product. I do NOT recommend buildbuck. The attachment points perform poorly when installing windows and finishing out the window opening. In hindsite I should have used treated 2x12