I think the reason your violin sounds thin & snarky outside is because there’s nothing for the sound waves to bounce off of, they just float off into space. Indoors, the sound waves bounce off the walls or get absorbed by furniture, carpet, etc., all of which affect your perception of the sound. I took my violin with me to my cousin’s house at Easter and I was surprised how loud it sounded. Of course it was all hard surfaces and no carpeting or upholstered furniture where I was, so it really sounded loud even though the room was big. You just need to get used to the fact that your violin’s sound will differ depending on what environment it is played in.