I train bis with back, and chest with tris, but also hit arms after shoulders.
On back/bi or chest/tri days where the arm muscle is already pre-exhausted I usually train with higher volume. It's hard to do heavy, heavy curls after rowing your ass off, so I get done with back and then do 5-7 sets with 12-20 reps for the bicep. Same applies for triceps following chest.
On shoulders day, though, I train arms heavy. 6-8 reps generally and between the two sessions per week my arms are right where I want them. (Okay, they could always be bigger haha)
Try it out!