Can you get proper imaging if speakers are not the same distance from center?

If it sounds good to you then it is good. You are obviously aware that this is not a preferred audiophile set up. The image should not be centered but shifted toward your nearest speaker.

If you want to see how much your image is skewed put on a good mono source which will be indicative. In a well set up system  a voice would be dead center.

If it sounds off and it worries you get some flavor of DSP that can set a delay on the farther speaker.

“if it sounds good, it sounds good”. This tends to be my inclination.
But I wonder if there will be a marked improvement if I move the listening position closer. I would certainly get a bigger perceived picture on the TV! But changing the furniture would be a big deal.

It may sound good, but, you never know if it could sound better unless you experiment with placement.  It would be incredible luck if you just happen to find the ideal spot without extensive trial and error.  Even if you are not perfectly centered and equidistant to the speakers, you can compensate, if necessary, if you have a balance control.

I personally think balance control is necessary for any system, even when speaker placement can be optimized,  I find that even a small adjustment makes a surprising difference.  When I had my Mark Levinson No. 32 preamp in my system (permits very small incremental changes in volume and balance), I could hear a .2 db change in channel balance even though a whole db change in overall volume was not easily detectable when playing music (steady state test signals make changes easier to hear).  I insisted on balance control (and remote volume control) on a custom built linestage built by a very old school builder who normally does not offer such features.

Audio is all about the compromise. Yes of course the sound will be better with everything moved around. While you are at it get rid of the TV, rack, etc etc. Then of course it will be better in another room. Knock down walls, building the room. Only to discover- guess what?- even that ain't perfect! Mike Lavigne paid a pretty penny to professional designers and builders only to open the next decade fixing what they almost got right. If that room wasn't good enough then for sure no room ever will be. 

So chill. Relax. Pour yourself a nice tase adult beverage kick back and enjoy the good life. Livin' the dream.