Cost based POC is probably the easiest and most widely used RA method in most countries where unrealized profits are allowed to be shown on fin. statements.
Three GL entries are all that are needed for POC calculations based on value (i.e cost).
1. Unbilled Revenue adjustments
2. Advance billing adjustments
3. Increase / decrease in Provision on Loss Contracts
The offset postings to BS are Unbilled A/R, Advance Billings and Provision for Loss on Contract. These of course reflect the corresponding Balance Sheet accounts for the P&L accounts affected by RA calculations.
The entry you are asking (capitalizing margin to Balance Sheet) sounds odd. To me, this seems calculated margin and should be posted to COPA instead. Hope this helps...