I agree with both of you. Go large and be comfortable. Make your stay enjoyable. I think even solo, a large one will give comfort. My preference.("food")You can stay dry with a fairly small tarp. However, I use a Spinn Big Mamajamba when hiking with a group and a Mountain Laurel Designs UL tarp (now discontinued) when solo.
The small tarp used correctly will keep you dry, but you have no room to cook and move around.
On the Colorado summer hang it rained everyday. I stayed dry, but the folks with the big tarps were making tea and visiting