Richard I think the last two paragraphs of your post outlined clearly what I was inadequetly trying to explain, most specifically this:
If it’s a full time job and you want to work part time, the likely result is the company will just look for your replacement. If anything, they are doing you a favor. Working part time, I would expect the company at best would keep your current rate and offer no benefits in exchange for the inconvenience of having to deal with part time work at a set number of hours.
My point about IAB’s suggestions for compensation was that it went against the grain of the question. Because his situation is known to his employer on so many levels it is disadvantageous. The only way it may work out is if the company places a lot of priority on fostering family environments and understands that OP is trying to do what’s best for his family and the company and is willing to strive for a balance, I’ve seen that in some foreign companies.
At the end of the day, business will go on with or without OP. What if he died in an accident? Does the company go belly up? Probably not. So unless you are that amazing at what you do, you can price yourself out of a job in this situation. This isn’t getting a new client, this is retaining an old one that knows a lot about you.