I don't know if this is common or not, but I have been fishing this little pond near my house and I have been having a productive (quantity-wise) using the same presentation. I have been drop-shotting a 6 inch dk purple worm from shore and I have been catching a lot of little basses.  All the fish I have been catching are almost exactly the same size.  I can see a good number of larger fish in the water, but it seems that all I can catch are the little ones. So my question is, can a presententation, even though a successful one, be limited and target a particular size of fish?   Are there any changes I can do to this presentation to catch larger fish? Or is it simply the fact that it is early summer and the most active fish are the smaller ones? Any comment would be much appreciated.

could be any one of  or all of the reasons you mentioned    try  upgrading lure size  and just be patient  remember worst case scenario   your catching plenty of fish    could be that the dinks are quicker to the punch also  the biguns   if you can see them chances are they can see you  and they are wise to your tricks      good luck

There's a high probability the bigger bass are feeding out of your reach. Try lobbing a jig under a slip float on light line, medium rod farther out than you normally cast. Your aim is to get a bait over a hole or contour break that might be holding the bass you want. Big bass in little ponds tend to learn about you and they will go away to a more secure place until they feel safe where you've been seeing them. If you see a big bass in a pond it's unlikely you will fool it into biting. They can hear and feel your shoes grinding the bank, and can see anything more than about 10 degrees off the bank.

Jim

Its true, the bigger that, generally the smarted it is.  They don't get big being stupid.  That being said, see if you can cast to them from a different angle, maybe from another side of the pond.  A larger bait usually means bigger fish, but that's not always true as I've caught some of my largest on grubs.  Try using a tube worm, throw it past the large fish, and hop it slowly to the bass.  Then when you are just about on top of the fish you want, let the tube sit for a second or two, and twitch it a few inches in front of his nose, until you're a couple feet away.  Reel it back in and try again.  At least that's what Shaw Grigsby says to do.  Works for me sometimes...