Is it simply possible ? Which way(s) should I explore ?
What addition time are you using ? Digestion? Rippening ?
To increase contrast you may try to make addition time well shorter, with also shortened digestion and rippening times, not allowing much grain growth and size dispersion or, better said, to allow a lower crystal size dispersion until you have the contrast you want without decreasing emulsion speed too much.
A pictorial emulsion consists in crystals of different sizes (and different ISO), as you have a variety of crystal sizes you increase emulsion latitude and decrease intrinsic contrast (beyond development degree adjusting contrast).
A microfilm type emulsion (ADOX CMS 20) is "monodisperse", meaning that all crystals have similar size, the more "monodisperse" the emulsion is the more contrasty, ideally a pure monodisperse emulsion tends to have "infinite" contrast, you have black or white, but not gray scale, for this reason CMS 20 (and ancient Techpan) required extra low contrast processing.
With that you'll also get an speed decrease, so you should balance what you do.
If not doing it yet, I'd recommend you to make a technical approach for those experiments, use an Stouffer T2115 to make contact copies, and calibrate your emulsion tests, use a cheap luxmeter with 0.01 Lux scale to have a good reference.
I was trying to develop the high contrast component of a DIY VC emulsion, and I made several experiments in that direction, but I made a temporary break in that project that I'll resume in comming months, playing with those factors it was the next step, so if you try that way please report your findings, it would be nice to know what resulted.
