Looking at different rocket engines, L/D(CC_length/CC_diameter) ratio of combustion chamber is very much less compared to Rocket labs. Even the modern age engines like Merlin 1d and Raptor engines seem to have lower L/D.
Also, with reference to this lecture notes, having lesser combustion chamber diameter/ lesser contraction ratio[Ac/At], will subsequently increase the velocity in the chamber making it difficult to maintain the chamber pressure.
How do the length of combustion chamber is designed usually? Is there any specific reasons why rocket labs have went with higher L/d