Since Gao Yi was the financier, when and how personnel would enter the field was of course up to him.
However, once on site, how personnel were specifically deployed and how firepower was set up had to be determined by the participating mercenary groups themselves.
Mercenaries exchanged their lives for money, and while paid to do a job, they weren't purely cannon fodder; thus, if Gao Yi were to put them in a position only to hold off death or use them as bait to attract fire, they would surely refuse.