Removing the sanitary cross would be a good idea.
Even with a fixture cross, newer toilets will skip across the fitting and water will surge up the other arm,
Which raise the water in the opposite bowl, and then when the water spills out over the bend, you lose a good portion of water that had been setting in the bowl.
I'm in favor of not using cross fittings at all when two toilets are being used.
Just to see what I mean, you can pull one bowl, and flush the other room.
You will see water coming up the other toilet arm.
Strange, but true.
Even with a fixture cross, newer toilets will skip across the fitting and water will surge up the other arm,
Which raise the water in the opposite bowl, and then when the water spills out over the bend, you lose a good portion of water that had been setting in the bowl.
I'm in favor of not using cross fittings at all when two toilets are being used.
Just to see what I mean, you can pull one bowl, and flush the other room.
You will see water coming up the other toilet arm.
Strange, but true.