even if you take the outlet pipe off and turn it upside down just for an experiment, that will tell you. on a surface-mounted shower this is often quite easy so worth a try. the instructions should tell you which side is hot inlet, so check that.
but you say hot flow is poor so that might be the cause. Usually on a combi the hot and cold pressure are the same so mixers are balanced.
if you have service valves on the shower supply, you can turn the cold down a bit (this reduces flow more than pressure and is not usually considered best practice, but is an easy thing to try)