There is nothing that suggests he does not detect them considering the first in cockpit shot we see is Han having a Radio conversation with one of the cloud car pilots I'd say he has detected them alright.

This a fine example of the all too conveinent star wars problem "it works because we need it to here but forget about everything else"

So you can add a contradiction to episode 4 Alderaan / Deathstar approach + death star escape and episode 5 in Cloud city approach

And later on when they leave cloud city and have to go back Lando also mentions tie fighters when they are miles away from cloud city that they have detected.

I just watched the clip on facebook again... And whilst I like the increased distance It's a shame to lose the falcon leaving the junk also as a consequence but nevermind.

If that periscope view of the falcon were added to explain Jamming the sensors and perhaps hacking the Nav computer then perhaps we could have both Falcon and Slave 1 both leave the junk seperately.... And that is my very last final thought.