I'm not going to be a stickler for this, because, just as you say, PbP makes it nigh impossible to not be influenced depending on who posts first. Ultimately, I do encourage teamwork. The only thing I'd call you on is if the group spends large amounts of OOC time discussing how to handle ROund #3 of a combat... your characters wouldn't have the luxury of doing that.
The way I see it IC is this: it's unrealistic for each round to be a specific set of seconds. You don't move 40' in a space of a few seconds, then stand and do nothing while others do their actions. It's all fluid, and as such, you would learn to interpret each others' actions. You'd be able to register that Shackler is maneuvering himself into some sort of ranged attack even if he doesn't technically "act" until after you. It's really my job to gel them together into narrative format.
