A 'line sight' is an invaluable tool for knowing where you are on the starting line. But if you get a line sight that goes straight along the line (from the committee boat to the pin), it may not be very helpful because in order to use the sight you must be exactly on the starting line. You won't be able to see this sight before the start (since you approach the start from below the line) and if you do see it, this means you are right on (or over!) the line. That will not help you approach the start.
A better line sight is one you get from below the committee boat. I call this a "safe" line sight because when you have this lined up with the pin as you approach the start, you know you are on the safe side of the line. If you are two lengths below the RC boat when you get this sight, you will be one length below the line when you're in the middle of the line and the sight is lined up with the pin. At every start I also try to get a sight with the two ends lined up exactly, but a "Safe" sight is usually much more useful as I approach the line.