In your pictures the one on the left is a Legacy which like the EMB-145 XLR has a additional center fuel tank. Embraer added a larger bumper on the underside to help protect the tank in case of a wheels up landing situation:
A COEX 145XLR and a private Legacy.
As for the Embraer on the right it must be a stock 135 which doesn't have a center fuel tank and only has a small bumper which is in the same location but much smaller:
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Photo © David Goose
145, you can see the small bumper between the main landing gear just slightly aft of the lower beacon.