To follow on from the 'paper seller' I saw in DecJan previously. I got short that spread today right before settlement expecting trading on the bids and anticipating a tick or two. However, it was like a western movie with dust clouds brushing along the horizon, he was nowhere to be seen. I quickly hedged with the 6 month DecJun and put in my bid to scratch in the DecJan with priority. Managed to get the DecJan back and make 2 ticks on the DecJun, so got out with a 1/6ish of a tick loss net overall.
However given that information I went long the 3 month fly DecMarJun which was at range lows. The settlement seller wasn't there so the DecMar area was not going to be supressed, it was at lows in a range so a long over settlement made sense as a high probability trade into the afternoon session.
For me these kinds of observations provide the most edge in my own trading with the spreads. However as bone pointed out the backs are really the most exciting part of the curve, there's a whole lot less competition and free trades being handed out left and right for a market maker.