A length of para-cord running through those loops, pulled tight, wrapped down the center pole, and tied off with some half hitches works too; the issue lies with the invariable wind lift. I prefer the centerline as it keeps the tarpped space more open. If there is a center loop on the tarp I do the bear rope pitch to tie that one off; there is a length of cord attached to the center loop on the tarp that has a prussic's on it...more adjustable especially if one is not using static line/no stretch.