Are transfigurations restrained by the Law of Conservation of Matter?

JK Rowling has said that Transfiguration is a highly precise and scientific form of magic:

"I see Charms as a slightly lighter subject than Transfiguration. [Transfiguration] is harder work. Charms has a little bit of leeway for more personal creativity. Transfiguration you have to get exactly right, so it's much more of a scientific subject." JK Rowling - Mugglenet transcript of Q&A at Royal Albert Hall - 2003

I think that magic would have to fit in with our world in a way that works and is not disruptive. I do interpret canon as demonstrating magic as an energy force, one that must be channeled in various degrees of precision and power. I do think that elemental displacement and mass matters in Transfiguration and similar magic and Potterverse in general; if it didn't, there would be no Splinching. Splinching implies to me that someone wasn't able to properly channel the energy that is magic and, upon Apparating, they did not create a large enough receiving space to accommodate their whole body at their destination point. That said, I think it's possible that when magic energy is properly channeled, it allows for a fundamental adjustment in mass volume, allowing Transfiguration of an object or person from large to small, and vice versa.

• Barty Crouch Jr. Transfigured Barty Crouch Sr. into a bone and buried him.
• Barty Crouch Jr. as Mad-Eye Moody Transfigured Draco Malfoy into a ferret.
• Horace Slughorn Transfigured himself into a chair.
• Professor McGonagall, Sirius Black, Peter Pettigrew, James Potter, and Rita Skeeter change into Animagi, both larger and smaller than their natural state.
• Hannah Abbott accidentally Transfigures a ferret into a flock of flamingos during her O.W.L.
• Sirius and Remus Untransfigure Peter from his rat form to his human form.

I found an interesting page called Wizard Science: Transfiguration that says it better than I ever could.