Two things to keep in mind regarding coaches....
1 - The room under salary cap on your team page is only in regards to the money that you can spend on your players. The money you can spend on your coaches is separate. When you go into the contract screen to sign a coach, look at the color bars at the top of the window. There you will see how much you are currently spending, and have available to spend, on coaches.
2 - Some of the best team owners in this site will tell you that the position coaches aren’t worth much at all as they have minimal effect on your team. Therefore you don’t need to spend much and it’s ok if their ratings aren’t good.
One question I have for you, the 1,984,500 you’re able to spend, is that for one coach? The reason I ask is because I see you have two openings for position coaches. I wouldn’t be concerned if I were you and had to split that between two coaches.
And if you really want to spend more money for a coach, then you’ll have to replace one of your more expensive coaches.