Couple of random questions

Just a couple of random questions. First, it's seems that the the GT+ combo is very arbitrary. I'll get more kills one time, and get less money than the next time when I get less kills. Has anyone noticed this. And the multiplier seems to change randomly. Is there any rhyme or reason to this? Also, what is the little red bulls eye that randomly appears at the bottom of the screen. It sometimes changes to an x. Anybody know what this is. Any insights are appreciated!