Digital BW, The Print

I'm printing with a 1280 with MIS pigs.  Lately I've been getting 
what I can only think of as an alignment problem.  
Sometimes around a figure, that is against a light sky, I will get a 
slightly unsharp edge noticeable around the figure, definitely 
looks like something is out of register.  I'm printing on 
Sommerset enhanced Velvet.
When I do an alignment utility, I examine the result with a loupe 
and make the appropriate settings, but still the problem.
I've been doing the alignment adjustment on regular typing 
paper, rather than Sommerset paper.  Is this the problem?
Thanks
David