And that is correct, the Work-in-progress account never includes any factor of income / profit.
The Work-in-progress account value gets transferred to the P&L Cost of goods sold. The sales price gets posted to the P&L income.
If you want to invoice the Sub 2 in proportions, then enter those proportions on the respective sales invoices, and the Work-in-progress will reduce accordingly.
Perhaps if you want to put relative values to the factors, then we can work through the mechanics.