W/A C/S Ratio

Hi, could anyone help me understand the below?

A company provides three different levels of customer service support for one of its software products. The following data relate to these three levels of support:

Support level Superior Standard Basic
Annual fee 1,000 750 400
Annual variable costs 450 250 180
Annual fixed costs
(see note below) 200 100 50
Profit 350 400 170

Note: The total annual fixed costs are budgeted to be $1,000,000. None of these costs are specific to any type of customer service support.

Assume that the number of customer service support contracts sold are in the proportion:
Superior 20% Standard 30% Basic 50%

The annual revenue that needs to be generated in order to break even is closest to?

The answer provided is $1,690,000.

Product Sales mix Contribution per contract Weighted average contribution
$ $
Superior 20% 550 110
Standard 30% 500 150
Basic 50% 220 110
370

Breakeven point in units = $1,000,000 / $370 = 2,703 contracts

If these are sold in the proportion 20%:30%:50% then this gives sales of
Superior = 2,703 × 20% = 540.6
Standard = 2,703 × 30% = 810.9
Basic = 2,703 × 50% = 1,351.5

Multiplied by the sales revenue per contract gives total revenue of
(540.6 × $1,000) + (810.9 × $750) + (1,351.5 × $400) = $1,689,375

My only question is, because it is asking for revenue required, why would the answer not use sales mix % * WA C/S Ratio?
I have a very similar question on the same exam and to get the answer you;
Get the sales mix of each
Work out the individual c/s ratio (EX Superior 550/1000)
Do the same for all three, add them together and then divide this by the total FC to get the revenue?

I just want to be sure I know the difference of when to use one and the other please.

Thanks in advance.