I agree with the OP.
The number of times I have seen Y pax drop a large bag into the J bins on the way through is more than enough for the FA's to be missing it.
If (and it is an if, more so than a when) I am in J, I want to be able to board later and get off quick, without having to stuff around looking for a spot for my bag.
There has been several times when I have had to call an FA for help, and they have had to move around other bags to get mine in...and J has been nowhere near full.
Could be a local thing, but I see this happening more out of SYD on an evening flight more than other places.
Making the FA's aware of it would help, but they are usually pretty busy at this time.