In my case, the trick was not to advance. Your own Brahmos are already within range, so there is no need to present yourself as a target. Form up into a tighter air-defence formation, and take some shots at the exposed enemy ships as you fall back a bit to wait for the carrier to catch up. Maybe have a shot at the docks with your land-attack Brahmos too. Make a determined effort to shoot down enemy MPA before they can spot you. Then, when you're invisibly hidden in the ocean, engage at your convenience as the enemy ships present themselves.
The SA-20 is definitely a pain, but not a show stopper. You've got 200 mile radars on your MPA, and the SA-20's only got a 110 mile range, so it can't stop you from spotting ships. It's a TVM system, so it needs LOS to engage, which means you can evade it at long and medium range simply by diving to min altitude and getting below the radar horizon. Your objective is to kill ships, not SAMs, so you really don't need to tackle it at all. If you really feel you have to engage it, you've got some land attack Brahmos, and the Harpoon IIs have GPS-based land attack capability. (A swarm of Harpoons acting as cover for the land-attack Brahmos is a great way to hit the docks, incidentally.)