Weigh the eggs first and match that weight with all your other ingredients. The best sponge I ever made was with Bertolli olive oil spread and not butter.
You can always try adding a couple of tablespoons of water/fruitjuice/milk when you add the eggs. A fan oven will dry your cake out more quickly - cook for 5-6 mins less than usual, when it comes away from the side of the tin slightly, it's cooked