I understeand that Romans preferred to fight in a "fair" fight, on plain field with their heavy infantry, no "tricks" like Hanniball's manouvers. Does this mean that when two Roman commanders collided they just sent their units in a standard formation to see who beats who? Wouldnt that always favor larger force?
Not true!
Roman armies had a kind of foreplay that lasted for days and even months.
During this the armies danced back and forth until one had even the slightest advantage, them attacked, as often, it was these advantages that decided the battle.
The battle of Pharsalus is an example of this as Pompey's army took refuge on a hill above Caesar's troops to hold an advantage.
Sources: Caesar's Journal