Yep! More players means more Omens, more Actions in combat, more equipment, etc.
It also means you have more room to play a bit mean as the GM. You can throw more dangerous situations at them, include enemies with strong attacks or nasty gimmicks, use cults that are tactical and smart, etc.
You can definitely reduce Omens if you want to, but my experience is that this makes the game feel a little more random. The fewer Omens the players have, the easier it is for them to get picked off by a couple bad rolls.
Also, some of this will depend on the tone you want to go for. If you like tense, desperate, anyone-can-die style scenarios, you might want to reduce everyone's starting Omens by -3. The current starting Omens is a little bit more geared towards adventure pulp.
I haven't experimented with this specifically, but if you really want Omens to scale with group size, you might try -1 Omen for all players per group member over 3. That'll give bigger groups an advantage in numbers, but anyone who gets isolated will be in more danger.