This is how I get a perfectly taut A-frame pitch:
1 – Stake 1 rear corner with your desired guyline length.
2 – Raise rear peak to approximate/visualize angle and height.
3 – Holding the peak in one hand, stretch out the other rear corner and stake it down symmetrically to the first. Leave rear peak unstaked for now.
4 – Go around and attach front ridgeline peak to pole and stake that out. Don't be afraid to really pull this outward tightly, I'm always surprised how much strength I can use here if my stakes hold. Your pole should kind of balance on its own now.
5 – Go back to the rear peak and stake that out, again really putting in some muscle to get your ridgeline as tight as possible.
6 – Finally, stake out your front two corners in a similar fashion as the rear.
7 – Stake out any side guylines you might have left.
8 – Readjust tension at any of the stake points.
Some things that help me do this:
– At the peaks, I let the guyline go up to the pole before going back down to the ground, instead of having the pole directly connecting to the tarp like it appears you do in your photos.
– I use Linelocs to adjust tension, makes initial readjustment and sag adjustment easy.
– For the corner guys, I angle them more to the front ends than a perfect 45deg angle.
– I use MSR Groundhog stakes for all my points. Small weight penalty, but man can I tug on that ridgeline without these budging.
I agree that you could start by trying out a tighter ridgeline, but accumulation of snow will eventually sag the large panels of sil anyway. Steeper sides can help with this, but then you obviously might have more exposed ends. In the real world you'd just have to periodically swat snow off.