Older series of the 3080 FE fits well with 2mm on the front and 3mm on the back. However some of the newer series uses a bit thinner gaps where 1.5mm works better on the front and 2.5mm or 3mm on the back.
Your best bet is to consider by manufacturing date or take apart and measure required pads.
For the backplate, even 2mm works but 3mm may have better contact. With 3mm on the back, you may experience that it gets a little humpy but you don’t have to worry about that. According to this 2.5mm may the best option there.
