First, the BPL bivy's are fine products.
Second, all bivys of any fabric or design will condense inside in certain conditions, MLD ones included.
My feedback from customers, my 25 year+ personal experience and from reading posts and info from many sources is that this is part of bivy life.
Some products are better than others. Some people fare better than others in the same product.
The only two factors in the bivys themselves are fabric selection and design.
Most of the UL and SUL bivys that use Silnylon, Nano, Cuben, SpectraLite(MLD comming in the Buddha Bivy), PU coated or other various totally waterproof bottom feature a simililar design of the bottom wrapping up the side. Most have the bottom girth match the top girth. This is because it is easier to build and so costs less. The roll widths of the fabric yeilds two bivy tops for a given length instead of one. The silnylon bottom is less expensive than the top. Maybe the new .5 stuff is the same or slightly more than the top fabric.
A more shaped top that would wrap down the sides farther require either a wastefull boxy/simple head and shaped foot design or more sewing and shaping. -More expensive.
The top fabrics are what they are...Pertex, DWR nylon, Epic, eVent, Gortetex or a range of other PU /Acrylic coated fabrics. Most are pretty good. More of it than the coated bottom will help some, but don't look for the holy grail of zero condensation. Obviously the more breathable the less condensation but it's a trade off with protection.
I have started to use less of the bottom material and more of the top. Instead of a 50/50 it's now closer to 65/35. One part than seems to make a difference is in the head torso area. More brethable there helps a lot more in percentage than in the lower part. makes senses as there is a lot more skin area to persprire. In my newest bivys the foot is still at 50/50 and the head more like 70/30 with the top of the head almost all breathable. I also use a drawstring foot for ventelation and since the top has a wider girth, the zip opening is wider and offers a wider vent.
A lot of designs are possible but I wonder if the market, which already has $250+ (under tarp) bivy's can support more design.
Weight is also an issue. At some point , for many, the weight became the holy grail of SUL as opposed to pure function. If the bivy can save an ounce of condensation or time to dry it, is it worth it? Tech exists to make sub 1 oz bivys but the function would be pretty rough.
Your feedback and open debate on these issues help drive companies to do better and we all owe BPL a debt for providing the forum. Thanks Ryan.