That may very well be the answer, but it looks to me like the result of the die itself. Perhaps a slight slippage when the hammer struck?
I've seen this on quite a few RR denarii, and my conjecture is that it has something to do with the engraving process. It looks to me as if the engravers sharpened the edges of the letters by filing away some of the metal in the fields around them. Or perhaps an area was prepared by filing before the letters were engraved? You can also find these "gutters" around the devices at times. My question is: how would you differentiate the ancient technique (if it existed) from modern tooling? For that I don't have an answer.
I have a thought. It may or may not be correct. I haven't had my coffee yet. If a letter is cut (engraved) into the die, the excess metal ends up on the shop floor. Letters are also sometimes formed with punches. When a punch is used, metal is not taken away, only moved, forming a sort of mound around the edge of the shape which has been impressed into the die. When the die is used to strike the coin, the letter, which is negative in the die, is raised above the field of the coin while the "mound", which is positive in the die, presses into the flan, leaving a depression around the edge of the letter.
