Yeah, for a fun try at the scenario two of the new Bulldogs and fill the 3 other slots with their locally produced Gladius Mk II. Nothing in those vehicles is going to penetrate the armor in one hit- the ERLL on the Bulldogs is still just 8 after all and the Gladius are full of 5 point hits. The Gladius would also have limited/decreasing firepower from the RLs . . .
Gives the Marian CO a bit of a catch-22 decision . . . wait for the Bulldog to get more ERLL hits and hope the Gladius Mk II's LAC/5s connect as well, THEN fire the RL15s . . . or go with the alpha to start the ambush and hope you put out enough damage to really weaken the Merlin lance before they can wreck the Bulldogs. Heck for the scenario I would even give the Bulldogs the advantage of being Hidden Units rather than just sitting in trees, so they get in their shots when they want to w/ less defensive modifiers.
Note, I am not saying those were the tanks involved . . . BUT it is a serious force, just not a big enough threat to a lance of heavies without something that can make big holes for the small plinker weapons to exploit. It would be a fun scenario to see if you could do 'better' than the sourcebook result.
I think one other question not addressed however would be what were the Marian commander's orders? Were they ordered to kill enemy units? Or stall/degrade their performance? If the orders were to delay the MAF heavy lance for X amount of time so other forces could retreat safely, load a DS, or position for a pitched battle . . . then the MHAF commander achieved a minor strategic victory for their orders.