When to Reduce from 2 inch

[aaronj8083]

So I have been reading and reading. Working on just finishing up the collection of materials. I want to make a simple pot still with a keg. Therefore, it is good that I already have 2 in copper pipe around the house. I already have 2 90's as well. I was wondering if it is acceptable to rise out of the keg about 12-18 inches then 90, carrying the 2 inch all the way over to the other 90. Once I turn down then start my reducing to a graham condenser. I want a fairly decent section of 2 in running away from the keg to separate the collection form the propane burner. Since I have enough 2 in pipe for this my question is is it ok to do this. I have seen other designs where it is reduced to 1 in right away.