I don't even try to attempt an answer to Heraklia's question: military matters are unknown to me!

But I can certainly pose a further question. Maybe, on top of higher soldus and various forms of bribery, might it be that Octavian promises to avenge Caesar played a role in legions abandoning MA for Octavian?

I mean, I do believe that MA was not honest in his reconciliation to the "Liberators" (but that's a personal interpretation). However, I do think that this attitude might have played well in the capable hands of young Octavian. I can picture him using MA's apparent betrayal of Caesar to sway the veterans into reading it as an actual betrayal of their late beloved commander as well as of the veterans themselves. Octavian might have used an argument along the line of Antony's words were of damnation against the "Liberators", but he did not ACT against the "Liberators", whereas I (=Octavian) will lead you to avenge Caesar's homicide.
What do you think? Might this have been a consistent enough leverage to sway the veterans?