you approach the jump point at a fairly high velocity so that you exit the point with a half decent vector, by the time the pickets can react, you're through. Also, there aren't really enough ships to put a 'small fleet' at every jump point. the main forces are going to be located in the primary battle zones to try and hold things down. at most there will be a space station in the system, or a picket ship meant to be a tripwire. Listening posts, etc..etc. They kilrathi actually start loosing pretty bad prior to the Battle of Earth because humanity is able to sneak their light carriers back behind the lines like Tarawa did at Vukar Tag. Thats why they sued for the armistice. This (at least in my mind) would indicate that the cats (and even humanity couldn't) cover jump points like your thinking.
another point too. The only time i would ever have my force positioned close to a jump point is when i know an attack is coming. For the most part a fleet that isn't directly engaged is going to be around an orbital facility of some sort, save on engine time and all that.
edit:
also, its standard operating procedure to deploy cruisers and destroyers and frigates and stuff first, to pull away the enemy force/tie them up for the carriers to come through.
edit 2:
the velocity thing, there is a 'safe' quick speed to hit the jump. i'm not sure what it is, but there is a maximum allowable to go through which preserves a significant vector for exit. i know kruger is pretty famous for it. he makes high speed (outside the regs high speed) jumps to quickly close distances, he did it at the battle of Earth. Also, Ragark had deployed his forces around the jump point which the Mjolnir (cat super carrier, bhantkara class) was going to take to escape. Kruger jumps in at a high speed and with enough vector to get away from the jump point unscathed. (fromt he novels Fleet Action and False Colors)