In an email relating to an order I placed with Phototex yesterday, in which I brought this forum question to his attention, owner Walter Gierlach was concerned that the possibility existed that maybe you were using solvent-based Phototex when you should be using the aqueous (water-based) variety for your pigment ink Canons?
BTW, although my initial post was (regrettably) sort of incoherent, I merely meant to say that I have always had the need to flatten the shadows of my bitmaps by about 20% to produce a result on Phototex that was comparable to more traditional substrates, its gamut being not as expansive in that tonal range.