I'm not entirely sure, but I think if ImgBurn does a Format before a Write to an unformatted rewritable disc, it does not eject the tray after Format is finished and before Write starts. I'm only going by memory here, but I think that's the case. If there's not such an option, I'd like for there to be one to eject the tray after Formatting is finished but before Write starts.
On my Pioneer BDR-209D, when it formats before writing Ritek 8x DVD+RW, it seems to want to fail on Verify. If I manually do the Format before the Write and let the program eject the disc after Formatting and then do the Write manually after reinserting the disc, it doesn't seem to do this. So, though it probably shouldn't make a difference, it seems in this case that ejecting after Format but before Write might make a difference for me.