I think I use a 5 egg mix in that size bowl.
Do you use a mix of plain and sr flour in your madeira? That does make for a very heavy cake ime.
My failsafe sponge recipe is to get the right number of eggs and weigh them with their shells on. Then use the same weight of stork/sr flour and caster sugar. So if the eggs are 245g you'd use 245g of all the other ingredients.
Beat the stork until it's soft then add the caster sugar and beat it for 5 minutes so it's very light and fluffy. You really need a hand mixer or food processor for this unless you've got very good arm muscles.
While it's beating lightly beat the eggs together with a fork and add a tsp of vanilla essence and a tbsp of milk.
Once the marg/sugar mix is beaten add the egg mixture a bit at a time with a spoonful of flour. Beat well after each addition.
Once you've added all the egg mixture stir in the remainder of the flour plus a couple of extra heaped tablespoonfuls using a metal spoon. You want to be fairly gentle with this bit so you don;t batter all the air out of the mixture.
Put it in the greased bowl with a small circle of greaseproof in the very bottom.
Before you bake it, wrap the outside of the bowl in several layers of wet kitchen roll then a layer of foil. This stops the outside going very hard and crusty.
Bake at 160 degrees for around an hour but possibly quite a bit longer - the middle of bowl cakes takes forever to cook properly, hence the wrapping around the outside.
I make that recipe for all of my sponge cake orders and I'm always complimented on how light and moist it is.