If you are looking at making your own router table top and using a Jessem plate then you might find these of use, they may fit Incra but @Peter Sefton would need to confirm.
https://woodworkersworkshop.co.uk/jessem-corner-levelling-pads/
Rather than route out a stepped hole for the plate to sit on just route out a hole and it now sits on these corner plates like the Kreg tables. From my experience they give a much larger range of adjustment albeit from under the table but those grub screws only have a limited adjustment range because they must not stand proud and in my case to short so I had to fit another packing piece.
https://woodworkersworkshop.co.uk/jessem-corner-levelling-pads/
Rather than route out a stepped hole for the plate to sit on just route out a hole and it now sits on these corner plates like the Kreg tables. From my experience they give a much larger range of adjustment albeit from under the table but those grub screws only have a limited adjustment range because they must not stand proud and in my case to short so I had to fit another packing piece.