Digital BW, The Print

Hello all!  Just wondering...  My 1520 causes the paper (EAM) to 
curl and has "waves".  I think this is because of the amount of ink 
in the dots.  Anyways, my 1160 doesn't give me the same 
issues.  Is it the way the inks are formulated?  The 1520 is 
running Piezography BW original inks and the 1160 is using a 
CIS with MIS FS-N.  I thought it was the dot size that the printer 
lays down, but could it be the formulation of the inks?  Thanks for 
your help.

Andy