I have often wondered about two features of C&O steam locomotives. First, the placement of the headlight. Why? Second, almost any of the types could have regular (often huge) tenders, or Vanderbilts. The reason for this?
Well the size of the tender generally had to do with the size turntables the railroad used in the area the engines would be running, and the distance between stops on the railroad. Obviously a large tender can carry more fuel and water than a small tender, so you can go farther without stopping for water or fuel. However, some railroads in the 20's-30's (or even earlier) found that when they ordered new, larger engines they had to get them with smaller tenders so they would fit on their existing turntables.
As far as headlights, I'm guessing that you're referring to the fact that some C&O engines had pumps on the smokebox door, so had to have their headlight lower down by the pilot steps?? It just depended on what the railroad wanted and what fit, many railroads did something similar (like Great Northern 2-8-2's and 4-8-4's). Some railroads like to attach headlights to the pilot section of a mallet, rather than to the body of the engine, so that the light turned with the pilot and followed the track better.