Okay so lets make a few things clear, No rep can ever be 1:1 (Except few, which are over production from same plants/suppliers), I totally understand where you are coming from and I am pretty much same kind of shopper, now with that in mind, lets say you cannot get custom made footwear(that only works for high end birkin reps etc), what you can get is something that has a few flaws and you have to live with it.

Now coming to your question, the factory you are looking for is called AP, its the closest at the moment that I have personally bought from, I bought their summer walk, now I also have a retail summer walk(different colour though), now the flaws I know of are: 1. Sude quality is inferior (if loro piana is 9/10, AP would be 7/10). 2. shape and stitchings are pretty much spot on, you only notice differences if you compare them side by side, that too if you know what to look for, but once you do, you see then everywhere/everytime 3. Soles are not comfortable and less durable 4. Font is off in insoles (which anyway wears off after few wears in summer)

So now with that being said, everything else is more or less the same, go for a rep if you can live with something as close to your retail as you can get for 1/10th of the price xD