Ok, after much experimentation and a fortuitous location of my rear feeder sheet guide (!) and a fair bit of wasted paper (thank goodness it's double sided, the matte) I've figured it out. I think you were right about the front loading automatically putting uniform borders around the image. With the rear manual slot, I'm able to get the original dimensions of the image in the 8.5 x 11 file I've created in PS. Maybe there are different ways, but if I uncheck
Scale to fit media and leave
Center image checked, it works. Attaching an image of my settings in case that helps anyone in the future.
I played around with Lightroom briefly tonight but didn't get as far as printing. Interesting points but I'm often working with an already saved PSD file that isn't in LR so I'd still have to import that then click on Edit in PS like you suggest. Also, it seems there are less control options. For instance, it just says "Black point compensation will be used for this print" without giving you the option to turn it off like in PS. I've read (here, for instance - a very useful guide to printing -
http://people.csail.mit.edu/ericchan/dp/Epson3800/printworkflow.html) that is should be turned off with Perceptual and turned on with Relative Colormetric. Now, I haven't taken the time, effort, paper and ink to test that but it's nice to have the option, I'd think. Maybe I'll play around with it when I've got more time but thanks for your input and advice, Dan - much appreciated!