Mainplate/Balance Staff Interaction.

One of the movements I'm trying to revive is an Omega 620 which the serial # pegs as a 1970 movement. The balance wheel spins but does not oscillate back and fourth. The balance is on Incabloc settings on both ends, however there is a small dome sticking up from the floor of the mainplate with a hole thru it for the balance staff to pass. The dome edges appear to have been nicked and it looks like the edge is pushed into the hole for the balance staff which may be my problem with the lack of oscillation.

I'm under the impression that an Incabloc setting is the only thing that makes contact with the balance staff when assembled. So what is the purpose of a dome feature on the main plate? If it serves no purpose would it be best just to take it off entirely instead of trying to push the nicked edges out of the way of the staff?

Archer,
The Incabloc settings are good. Its the question of the bump on the mainplate. It doesn't appear to serve any function. Unless I'm looking at it with not enough magnification and it is actually the setting instead of part of the mainplate.