I have a Brother MFC-J6910DW printer which is a large A3 capable inkjet with duplex printing which I use for printing orchestral/band parts A4 on A3 sheets in booklet format. The only drawback is that it needs a 20mm clear bleed on the front and back edge of an A3 sheet for paper handling when it is printing duplex. To compensate for this I set up my pages as mirrored pairs with 22mm as the outer margin and 10 mm as the inner. This worked with sibelius as far as page setup was concerned but as sibelius never seemed capable of booklet printing with the Brother, I used to out put to PDF, load the PDF into a template in Adobe In-Design and use the In-Design ‘Print Booklet’ facility to print.
I thought that Dorico with its inbuilt booklet facility would improve on the steps above above but I have hit a snag. I have set Dorico up to duplex print A4 sheets in booklet format on A3 paper. I have set up mirrored margins of 62pts outer and 28pts inner (I calculate 1mm = 2.8pts) in page set up. The visual shows the correct imposition with the correct mirrored margins however when Dorico comes to print the whole image is offset approximately 26mm to the right on the page. This means that the right hand edge of page 1 goes into the 20mm no print zone truncating the last bar or so of every stave and the left hand edge of page 4 has a huge margin ( it is only a four page part). Similarly with pages 2 and 3. Either I am missing something fundamental (unlikely as the graphic representation of the printed page is correct) or the printer has certain characteristics which Dorico doesn’t pick up. I don’t have any problems printing booklets with In-Design.
I can always (and have) output to PDF and print via In-Design but it seems a pity.