I purchased a pair of JBL monitors with 5" woofers a few years back. However, I just couldn't get use to them. It appears that I don't like the sound of rear firing ports. For me, I tend to hear some type of time delay in the sub and low frequencies. It also could be some type of issue of the subs and low frequencies bouncing off the back wall, as well.
My monitors are 12" from the wall and are at the proper height for my listening position. I haven't been in any studios that have monitors with front firing ports, therefore, I can't be sure if it's the monitors or my ears. However, I can mix with headphones without any issues.
I have a very nice headphone setup and get a good speaker translation. Most people can't tell if my mixes were done on headphones or studio monitors. However, with that said, monitors are very useful to double check that my mixes are pushing enough air. That is one thing that is tough to judge when mixing with headphones.
My headphones came with a calibrated plugin which is within 0.5db flat throughout the frequency response. When I have gone through some of my old mixes were mixed with monitors, I hear a lot of stuff that needs to be addressed with EQ.
I know that mixing with headphones is usually frowned upon. However, using them to mix, is becoming more popular with plugins that emulate speakers, and high tech headphone amps.
I'm interested if other people have had similar issues using rear firing monitors. I am also interest from hearing for people who use quality headphones for mixing, as well.