Hello Lech,
Yes, they all look alike, but then maybe they are all draped and cuirassed. Perhaps it is only an unusual way of engraving the cuirass from this angle though. However, I have seen a few of the Constantine I & Licinius I examples with B5 busts and they are clearly different from this coin, with no trace of drapery, but the Caesars are profiled a little differently. I guess that is why Bruun said "Bust B4 or B5, a matter of opinion" as he couldn't make up his mind.