How tall do 'Romaescu' grow?

The reason I ask as that the ones I have planted out have grown as tall as
my purple sprouting broccolli plants - about 1 foot. I can't see how the
great heavy heads are going to be supported if they carry on growing at
this rate.

When I tried growing them a few years ago, the seeds in the packet did
exactly the same thing and no heads appeared, just loads of leaves. The
seed company replaced the pack, and those seeds did grow differently - much
lower, but unfortunately the 'pillars attacked them and devastated them
before they were large enough to pick.

I have my suspicions about this seed packet, which is the same (well known)
seed company. I'd be grateful for any help.

Ros