My own personal headcanon suggests a semi-hard limit. That once the K-F drive gets to a certain mass, its inherent gravity starts to interfere with the operations of the jump (which for some reason stands at the arbitrary number of 1,131,250 tons). The other parts of the warship and attached dropships (even if there are fifty of them), are not dense enough to meaningfully effect the jump.
Now for the "semi" part, it means that technically a larger sized warship could be built, but the K-F drive would suffer damage with each jump. One could theoretically create a truly massive warship, as long as they were willing to repair the K-F drive after every jump.