Accumulated Cost for work order with partial completion

Dear Community,

We have scenario where we have setup Perpetual Average Costing with Provisional Completions "Value Using Accumulated WIP balances" for Discrete manufacturing.
Material issued and completions are at different time. with all this, 1st completion is fine and system calculating desired unit cost. But system generating variance in 2nd and 3rd completion.
Please see below details -

Why 556.94 and 334.67 is coming instead of 510.80 and 290.10 respectively 90.72 is coming as WIP balance?

Thanks,