I believe I understand; the baseplates are angled, so it looks weird that the ground seems to be pointed and the background just randomly starts around a corner of the ground. The only solution I could think of would be to put trees or a wall or something in the back of the baseplate. Out of curiosity, does it have to be completely in the open? If you want a field, you could have grasses sticking up or possibly an old wall in the back; if it absolutely has to be completely blank and open, then the only solution would be to either try and copy and paste (in post production) half of a baseplate to make a strait line (not recommended, would be quite difficult and time consuming), or just get by without any angled shots that include the edge of the baseplate. It really makes a difference exactly what the setting is, and what's going on in this scene.

You are forgetting Rule #1 about backgrounds: You must cover the place where the background and the baseplate meet. If you don't, it makes it look like the ground drops out. Does it look like that in real life? No. I would advise not using a green screen. Use a blue sheet of paper for a sky background. That way, you don't have to go through all that keying and color correcting and all that.

If there are trees, you can cover up the pointed end. Small plants, brick-built trees, bushes, a few fallen logs; it's doable, as long as you have trees already there, you can easily just add more plants and whatnot to cover up the area.