Saramc, it depends on the growers choice how tall he wants his plant.
Once top is severed it will develop shoots near that point and some down lower one can create a rather nice canopy from them to develop a nice looking plant in tree form.
You just pick and choose as you watch the new form shoots grow as to which to keep.
I grow in containers and favor tree form or the "slingshot" form i call it.
You ask
And if you do that, not to sound stupid, but the tree will normally gain in height with the next years growth, right?
To me no stupid questions from someone basically just starting out.
same year you can get height if thats what you want simply because one or more of those shoots will point upwards and some will be growing sideways .
By picking and choosing you can shape a canopy.
Fertilizing a tree also can have big effects on fig trees growing in pots. Nitrogen can make a fig tree grow quickly but can also harm it if given late in season.
Fig trees can be manipulated in different ways in my experience growing in pots, bush form , tree form, larger figs by certain ways of pruning and also to make sweeter figs or less sweeter figs.
You want a sweet fig raise up the ph.
Grow a fig in real acidic soil and it will produce but figs will not be as sweet.
General rule is first year fig trees usually dont produce many figs .
Some second year trees of mine did well producing several dozen figs and third year they did very well.
Not all fig trees are created equal though in growth habits .
There are the exceptions as some figs trees just are slow growers at the onset , then some just want grow to the sky which have to be taken care of in ones climate before cold season begins or there will be damage in storage.
Little by little as you get familar with your trees you will see how they respond to certain things you do to your trees.