Vertical banding on smaller prints

I have an Epson RX700 printer, maybe not the best choice for top quality photo's but it does print as well as my previous R300 photo printer. My problem is when printing on 4X6 paper I sometimes get vertical banding. I have set the printer up for alignment, and it prints perfectly on A4 sheets with the same photo's, so why the banding when I reduce the print size? I would be grateful for any suggestions, Steve

It may depend on "how" you size for printing.

Using Print with Preview is the best way to print from Photoshop. It gives you options for sizing the image and for placement on the paper.

I would never use Image->Resize for printing, nor would I adjust the number of pixels or the dpi of an image for printing.

Are you using the same paper for both?

This happens when printing from photshop or direct from windows, I do not rescale the prints, I let the epson software do that when selecting the properties, and yes the paper is Epson Premium Glossy for both A4 and 4x6. To be honest I would be more worried if it was happening on the larger prints, the 4x6 I really only use for proofs of for general pass about pics. Many thanks for you your input so far.