I would say that size tarp is a little tight. I've used that size before (it happens to be the size of my poncho) it's OK but tight. I've used a bag cover in the past in conjunction w/ this size tarp. A bag cover is not a full-blown bivy but will keep wind blown rain off of your sleeping bag. They are also lighter than a bivy and I think more breathable. I like my 8'x10' (appox. 2.5mX3m) tarp the best. I would not bring a bivy for this size tarp. Remember tarping is fun but site selection and orientation is critical.