Random shells aren't going to lead to TK penalties.  Since you don't have torps as well, we can rule out any reductions.  Seems a bit low but I'm not exactly sure what you should be getting.   I usually look at it this way though:  GB for XP, Blitz for playing.

Auto FCS lowers XP.  5K attack isn't going to yield much if any XP.   There are other factors like the type of ships in your game.  Having a BB/CV on the opposite team will increase the XP ~ generally you would also want to hit higher tier ships like CAs etc.

If it makes you feel better, I did 19K attack on a loss and got 800XP on a sailor...

I use manual fcs.  Also, how would I get more exp in GB?  For example, I assume I would get a lot more attack in blitz than I could in GB because in GB the battleships would probably just snipe me before I could do any damage. 

in a CA ... you'll get more exp just showing up in a GB then you will on average winning a blitz

I am in a CL, and I just got 17k attack and won and got 3k experience, the same as when I won with 5k attack.  Also I played a GB and didnt get any attack because they can just snipe me before I can reach them, and I got about 500 exp.  What would I have to do in a GB in order to get experience?  Does AA give you good experience or is that just credits?  I actually dont have any aa gunners anyway so that wouldnt really be an option but just curious.

Score the most attack in the room via only the highest level ships of the enemy team.

This will give you the highest EXP possible per room.

In Great battle, you would have to be patient.  Also, you need to get at least 1 attack to get a higher share of the XP.  Waiting until there are fewer ships will greatly increase your chance of doing attack.  So there's the trade off.  You can actively play in Blitz and get less XP or wait patiently and be less productive but get more XP (usually).

AAing is by far the easiest, safest, and best way to contribute to your team in GB for lower level ships. Once again, all it takes is one plane to get fair XP.

It might be frustrating but you might be better off playing blitz and getting less XP.  By actively playing and learning, you'll be a better player in the end.

ig you are dd, Cl in gb rooms the best thing  to do is find a spot you fit in to well... AAing ASW  or troping... Depending on your ship.   DD's make great ASW ship becuase you dont need sonar.
CA can set up with both AA guns and Run main guns for those pesky little dd's that decide to race across the map and bother the bb's or cv's.
    Only once crew i have build stayed in Blitz rooms till lvl 60.  Blitz;s a re good for credit and points, but other then that the Xp has always sucked. I can rember when getting 45k attack and only 5k Xp....

    Now if you have the chance to shot higher teir ships is were you get best XP in Gb rooms.
ie... bb1 shoting bb1 = crap xp
       bb1 shotting bb3  = x3 xp  

one thing i suggest is use  higher lvl gunners then the guns you use. + 10 lvls make for best  results of guns....

You always get some experience but once you do at least 1 attack, you get what some might consider "fair" XP.  In something like a CL, you probably won't see much difference in XP between 100 attack and 10K.  I think you'd have to do a significant amount to get a high amount.  But as I said, compared to zero attack, doing some attack increase your attack.  Also remember that staying in the game longer can increase your XP because your team has done more attack to the other team thus increasing your portion of shared XP.  Aiming for higher tier ships is always better.

If you're asking for the exact math, you likely won't find it.  Just try to get at least one attack, and win.

Do note that although GB might give you more xp, it doesn't give you as much credits as Blitz ( unless you do good with AA).
Unless you have outside credit sources ( fleetloans, rolling sailors and selling them) you will not get enough credits to buy new ships when they become available to you.