It depends a bit on the device type and printer. When you print from SAP via e.g. a PCL device type, the actual print depenmds on the fonts installed internally in the printer. The size of the OCRB font can be seen in SE73 -> Printer Fonts -> <Device type>. But SAP just sends a command to the printer to select ths font internally in the printer.
If you upload a true type OCRb font via SE73 -> button 'Install TrueType Fonts' and use this font for printing the OCRB characters, then the preview and print should look the same.