Bins aren't taperd in heighth, they are tapered in length in the first bin and last bin because of the fuselage.

Putting bags in wheels first allows for three(3) bags to fit instead of just two(2) bags to fit...thus, allowing more bags to fit into the overhead bins.

As for the assumption from what people have said about the handles on some bags being too long, there are very few bags that putting them in top first helps in getting them to fit lengthwise into the bins....unfortunately, the bins will not close.

(haha-ot) had a guy today in business class put his bags up into the bins. I didn't see him put them up, but after I made my pre-departure P.A. about bags and such, I came out of the galley to pick up coats from my first class pax and saw two bags protruding terribly out of the bin. Obviously the bin would not close with the bags lengthwise as some of the newer bins would.

I asked whose bags they were....he answered and i asked him if it looked like the bags would fit....he answered honestly and said yes....and I showed him that the bin would not close....so moved the bags around to fit....

The bins work if people actually did what they are asked to do during boarding.