Just saw this question a month late.... sorry.
The vinyl tubes finish the pressure treated 4X4's and make them maintenance free. Raw 4X4's are really pretty rough, often twisted and flawed and do not hold paint well. So the tubes are the 'siding' for the posts. They are nice but not cheap at $180 each.
The posts on the front and side of the porch only have 1/2 their length covered in tubes because the bottom will be a wall where the 4X4's will be covered. This allowed the tubes to be cut in half and one tube to be used for two posts, strictly a money saving maneuver.
The side of the porch / house has three full length 4X4's, with covers, that will not be covered. So they are covered from <almost> top to bottom with vinyl; a finishing trim ring, also vinyl, will provide the disguise at the top of each post so the gap cannot be seen.
The contractors have been off on other jobs for the last two months but are scheduled to return this Monday, 4 June 2018 to start siding the entire house as well as trimming- out doors windows and everything else needed to complete the siding. So with a little luck and some weeks, we may, just maybe, have something that looks like a house again, at least the outside. The inside is still a 'stick forest' of 2X's.
Brian
What's the purpose of the wrap around the 4x4's? And does it only get applied to the upper half?