Ok I developed the prints : I began with a bad frame which contrast was really low, but it was probably underexposed. Then I tried another two which were perfect. Seems like the processing is ok. Still have to get the exposure correct...I wonder if the problem isn't more the exposure. But I guess it's better to have no white spots (transparent spots) and high density rather than many white spots and low density...
Edit : forgot to say that the two good prints were made at grade 2 and 3. I see it depends a lot on the light and exposure.
Well more exposure tends to compress the shoulder and place more of the image higher up the curve. You don't need super dense negatives to get good prints but, and wholly dependent on subject matter, good exposure with adequate shadows always helps.
If you're attempting to make APX look punchy and contrasty it simply isn't that kind of film. It's emphasis is on midtone tonality. Sure it can have some contrast but it won't be Tri-X or Neopan.