I have tied smaller roast together with relative success, however, there is a tendency for the roast two separate slightly as they cook. This can create a gap between the roast which can cause the heat to penetrate between them. This becomes an issue when you are checking for temperature as you might be tempted to test it in the center which might be where your to roast come together which could lead too a misread in what the actual temperature is. That being said, I've also smoked the smaller roast with good success, however smaller roast tend to take longer per pound than larger roast.
