Is it the front shock that determines the ride hieght.tried higher springs as these old ones were too low bottoming out the swivel knuckles.

What

Which part are we on about?

Springs determine height. Unless its a adjustable coilover and the adjuster on the outside does.

If the car is lowered then you fit shocks with a shorter ram.

For example: If you fit 60mm lowering springs but use the standard shock then the ram has less travel due to the lowered vehicle and bottoms out on bumps. To cure this a shock with a shorter ram allows for the extra travel of the ram when lowered.