Lewis, going deeper while diving FRC is all about 4 things, making the chest more flexible through stretching and diving a lot, relaxing the chest cavity so it can get smaller, easier, getting the lung tissue used to(and more resistant to) negative pressure, and improving the speed and intensity of blood shift allowing more blood into the lungs, effectively taking up air space so that you can go deeper. All of that is easily accomplished if you are diving FRC 2-3 days a week, or being diligent about dry exercises. 30 meters with half a lung full is very doable for most divers, but it takes a long time to build up to. Extremely talented and experienced divers have done very deep FRC dives, like 80 meters+.
Be careful exploring FRC diving. Its a great way to dive, but must be approached cautiously. I'd recommend not going below a half exhale, at least until you are very experienced. At lower levels of exhale, squeeze comes on very fast.