This advice is probably too late, but keep in mind that the Vtails that are at 45degree angles naturally give more rudder area than needed, or less stab area, depending on how you size them. OK, that wasn't very clear was it.

Most airplanes need far more horizontal tail area than they need vertical tail area. And a Vtail with the two sides at 45degrees provides equal areas for rudder/stab. One way to deal with that is to flatten out each side of the V. Instead of a 90degree angle between the two halves, you go to 120 or so. That gives you more horizontal surface effect and less vertical surface effect.

Since the topic subject is Vee Tail sizing, I figured I'd throw this in for people who're designing to consider.

I figure you aren't planning on rebuilding the whole empennage, but there always is a next time.