thanks for the explanation, and as others have said the setup looks great! You may already know this, but i will share it for the benefit of others, my couple recommendation for what you are trying to achieve would be a more upright pot than the spherical pot. The roofing effect that the upper part of the sphere has, itself causes some of the premature condensation that you were referring to, especially with high grade copper. 4inch on 50 litres is very generous and it wont allow much pressure to build creating a temperature variance due to the lack of back pressure, which again can contribute to a cooler top of the pot vs bottom. A simple way to over come this is to insulate the upper part of the pot above the waterline so that the temperature of the top of the pot remains high enough not to allow condensation.
The other point to keep an eye on is the distance the steam is travelling before it reaches the first ring of the cooling coils and having enough flow to ensure the oil doesn't clog on the coils.
good luck and keep us posted!