ground cloth

You want the ground sheet to be smaller than your tent footprint, if it's larger and sticks out the edges it will allow rain to pool under your tent beneath the ground sheet and tent floor. About 2" in from the edges of the tent floor on all sides should do it.

I stopped using ground cloths. I figure they are unnecessary extra weight. In the past my tents always were replaced for some reason other than a worn out floor, but if a tent floor did wear out, I'd first patch it, then start using a ground cloth only after the floor was too shot to effectively patch.

Oh and to answer the original question, when I did use ground sheets I always went against "conventional wisdom". I agree that you don't want a ground sheet sticking out, but I always cut them slightly on the big side and then tucked the excess under. That seemed to make it easier to keep the tent bottom off of the mud during pitching.

I have a floorless tent. I have the smd haven.

I would think your answer lies entirely in what you want in your groundsheet then. As long as you do what others have said and make sure that it's not extending past the walls of your shelter so it won't collect rain falling off the walls. The question you have to ask yourself is if you want the groundsheet to just protect your sleeping pad/bag/quilt/whatever you use or do you want to be able to put more of your gear on the groundsheet and out of the dirt. I imagine some will tell you not to waste the weight on the extra fabric. I personally would sacrifice the extra couple of ounces and have all my stuff out of the dirt. But then again I am nowhere near UL weights let alone SUL weights.
You just gotta ask yourself what you're hoping to accomplish with your groundsheet and go from there.

I like big ground clothes so I can create a living space to stretch out/relax/sit and keep my gear clean and off the wet and dirty ground. Just my preference. Some people use full length pads and ditch the ground sheet all together.