Low contrast prints can be due to low scene contrast (ie; the lighting), or printing on too low a contrast grade of paper. The other factors that will result in poor contrast are related to developing of the film, but we will assume it is processed properly since most labs can do C-41 without huge errors.(posted 9404 days ago)Filters can help scene contrast but it's difficult to determine if in your case it's an issue. Filters are most dramatic with sky and clouds, less so with foilage, even less so with skin tones.
Kodak T400CN is no more a "low contrast" film than standard Tmax films or any other negative film. I would bet (in fact I'm virtyually certain) the low contrast prints are due to poor printing . Rememeber that automated enlagers also aim for 18 % gray. Operator overide can adjust print contrast and exposure if the lab/operator knows what it is doing. Find a good lab, or have them printed on graded black and white paper.
BTW: My local lab often prints T400CN too high in contrast. Kodak isn't stupid....they spend millions and million before a product goes to market. If there is a problem with film don't switch films switch processing. Anything put out by Kodak, Fuji, Ilford, Agfa in any speed or type, just like any modern camera and lens of any sort or style, can outperform anyone reading this forum.