The photos on Parkers show a full-size bike in the boot, wheels on (which the Octavia will also do, same platform) – so better than most at that size.
What are you carrying? I have a Honda Civic and the huge (485l), wide, low boot, completely flat load area with the seats folded, and the "magic seats" (they can flip up, cinema-seat style giving a huge space in the back to load) makes it far more useful than my old estate, especially when you need to carry 3 people plus stuff.
I scuba dive, and managed to get 3 of us plus all our UK kit (so 6 x 15l cylinders, a few boxes and a load of bags) in just fine with the boot and one of the seats flipped up. Nothing above the window line at all. Also managed 3 with bikes inside, with a bit of juggling and removing wheels.
All that in a car that's the same size as a regular Golf hatch. It's ace.