The problem last night wasn't necessarily the formation, or the subtelties of it, for most of the first half, it was that we couldn't keep the ball, Roma were at us so quickly once we had the ball, our passing went to pot, and we failed to retain the ball until the final 5 minutes. Navas worked hard, but he was a part of the problem, much as he was against Bayern at home last year, when he offered little support to Zab, while on the other side silva offered little help to Clichy, who was having an off night anyway, and it was clear after 20 minutes that we needed to change something. We'd had enough warnings by that point that Roma were a good side, pressing hard, and giving Yaya, and Fernandhino in particular, nowhere to go. The two up front also worked hard, with lots of making of space, but they needed to do more of their shift in midfield, and neither did, and while the space they made was good, we rarely had the ball to utilise it.
Milner made us better, Lampard made us tick, and Roma knew it, so they pretty well reverted to being "Stoke" in the second half, to preserve their point.
On top of that, we gifted another team a goal, where they had to do little or nothing to score it, which is pretty frustrating too.
Like you I'm not that worried about formations, but players need to do their jobs better, and one thing we are normally good at, but weren't in the first half last night, is keeping the ball, even under pressure, and we weren't helped by a couple of players being well off their best, especially in the passing department.
I can see us winning out there, because we will adapt the way we play, and we're unlikely to pass the ball as poorly as we did for the 25 minutes after we took the early lead. I also don't think Roma can improve much, but I know we can.
Long way to go in this group yet.