When I'm in a pace line on the flats I look at cadence before I take my next pull and match the cadence to what the guys ahead of me were riding. Riding off the front makes the 2nd guy do more work to catch catch up, or they will just leave you go. I've got a riding buddy who brags about not needing our using a computer, however, he is a terrible rider to be behind in a pace line, since he always speeds up the line on his pulls. From your post it looks as if the two riders in front of you didn't keep up the pace and after you took the lead the rest of the pack rode around the two or waited until they cycled back. Weaker riders who can't pull the line need to pull through without doing any work to keep from breaking the constant speed of the group.