Got to be careful with those graphs, because they are statistical, and good statisticians are good liars.
I had a contractor bleating about his woeful margin on what was quite a big contract, and showing me a balance sheet of around 6%.
I homed in on a couple of contract variations, which included things like chainblock hire, @ $300 per week (in 1997). For weeks on end.
First question, why hire, and why at such ridiculously high rates, when the equipment could be purchased for around a week and a half's rental ?
Company policy, and the hire company is a subsidiary to the parent, so we've got no choice on who we go to.
Exercising a right under the contract, I told them to buy the gear, paid them 10% on top (took ownership at the end), saved thousand of dollars, and made the contract more profitable...which they hated, as the profit was supposed to be smeared through the company and it's subsidiaries while they cried poormouth.