If you put a fallen guy on the base it established scale well. I did this on two of my Riptides.
Green has a little diorama on her base complete with a wall, some fallen combatants and a survivor hiding behind the wall, and Pink has a wounded Space marine crawling towards a shrine. No mistaking they are large ladies with that going on.
Don't forget structure when designing a dynamic pose, it is sad to have to reinforce a pose because it starts sagging because you gave it too little support trying to look dynamic. I had this trouble with the Blue Riptide.