Note that the scene where Brett is taken has some significant alterations in the DC compared to the Theatrical Cut, as described in this Wikia:
Immediately after Brett is taken, the theatrical version shows a closeup of Jones nonchalantly watching as Brett's screams fade. The Director's Cut instead shows Ripley and Parker running into the room in response to his cries. They look up and Parker realizes some of the drops pouring down on him are blood, which stains his shirt. He drops his cattle prod in shock. The closeup up of Jones is then seen, but instead of hearing Brett's death cries over the shot, we hear Parker calling out Brett's name.
The scene after Brett was taken is extended in the Director's Cut:
Parker: Whatever it was, it was... it was big and...
Dallas: You're sure it took him into the air shaft?
Ripley: Disappeared into one of the cooling ducts.
While Parker and Ripley arrived after Brett had been taken, they obviously saw the aftermath: the alien had taken him upwards and his blood was dripping down on them. It had to have been big enough to take a grown man and hoist him up and do this quickly.