I had to cut the first side down to match the length of the second one, and I'll have to reattach the beak on that side. This means that the main body will only be about 7.5' long instead of 8' (it was a bit over-sized before I had to cut it down), with a total ridgeline length of about 122".
I'm curious how you are attaching these "beaks" where you can remove them easily. My experience with space blankets (LDPE) is once taped, you rip and stretch the material when trying to remove the tape. Are you using mylar blankets instead? If so, just know that if you get a puncture you could have a catastrophic failure.
An A-frame with 10' ridgeline is more than sufficient if you know how to pitch it well. Most would have the foot end (windward) lower so protection is greater. Those with a bivy get by with as small as 5x8 tarps.
BTW, the reason you don't normally put cat curves on plastic tarps is the material doesn't stretch. For silnylon and spinnaker it helps keep the pitch tauter longer but you may still need to tighten lines, esp if it rains. If you still want to go through the pain of this, a few inches should be fine for 10' ridgeline.