Morale plays a large role in determining if you can take the hex, however losing a large number of men in the process indicates that you likely had a poor assault factor compared to the enemy. Given that you had superior numbers and you wound up losing four men to the enemy's none, it sounds like you either had extremely bad luck or else there is a significant reason for the poor outcome.
- Are you assaulting uphill? I ask because I believe that halves your assault factor (e.g., your 9 men suddenly just equate to only 4.5 men) and this would be my best guess as to what is happening to you. Avoiding uphill assaults is easily one of the most underappreciated element of assaults. You need overwhelming numbers to assault uphill and it is best to avoid doing this if at all possible.
- Are there any vehicles in the attacked hex? The vehicle's armor rating plays a huge role in assaults. (For instance, you can easily lose most of your men if you are foolish enough to try assaulting a M1 tank.)
- The state of your units also plays a significant role. I believe the assault factor is halved for both Disrupted and Pinned units. Which means even though your enemy's assault factor is halved due to being Pinned, yours would be as well if your units are Disrupted.
- Also the weapons being carried can influence the outcome to a lesser degree (each type of weapon has a different assault rating). For instance, I often find it very hard to assault enemy units that are carrying RPGs.