Ex is claiming spousal support. Does the fact that she's working full time and will receive in the region of £80,000 from the sale of matrimonial home (her half share) negate the need for spousal support.
Spousal maintenance is based on demonstrable need and the other party's ability to pay.
Without knowing a bit more about the financial details it is impossible to advise further.
As a general rule SM is falling out of favour.
It's only what her, extortionate costing solicitor, is telling her. I know you can give her more for a clean break divorce. I saw something where it's 40% of my income less 50% of her income which works out about £160 a year. That's what expensive solicitors get you.!!!
I'm not sure about your calculations above, I haven't seen that formula before. It does sound like she's quite a high earner then, and she may struggle to prove a need for spousal maintenance.
If getting 50% of the property is a good deal to you, why don't you offer that with nominal spousal maintenance on top? In case that is enough to get the deal done? It might just be enough security to satisfy her incase you suddenly got a big pay rise and she lost her job.
Would you take on a mortgage with high enough monthly repayments to mean that if she applied to the courts again, you had enough committed outgoings to make SM out of the question?
This isn't advice by the way, I'm not qualified to give that. Just an idea.