I could never use this frame. The reach is extreme for the sizes. And seat tube and head tube is very short for frame size that would possibly fit. Also quite big size steps between the sizes. Shame, because it really looks nice - and I do like that the angles does not change between sizes.
Reach wise it's not too different from the tideace gv201, but at least the stack is not that low.
If you have a look at how the mondraker arid (same geo) is assembled, they use 70 or 80mm stems.
I think longer reach and short stems is a good combo on gravel bikes because the short stems gives back a bit of reactivity that you'll lose when slacking the head tube angle, and I want an open head tube angle to avoid toe overlap and have some more stability at slow speed when offroading.
As for the short seat tube, I agree, for an AERO frame I'd like a more horizontal top tube, that will also give some more space inside the main triangle for a frame bag, having a lot of seatpost sticking out should help with comfort though.
I'll see how it'll look when finished