Earned Value for a task with non proportional costs

I have a question regarding EVM. Suppose I have a task with a 2 weeks duration. PV for week 1 is 800 and PV for week 2 is 200. If the PV is not proportional with the % complete, so each week I expect 50% of the task done, and suppose after the first week the % complete done was 60% of the total task. In this scenario if i use EV as (real % complete * BAC) I would get 600 (60%*1000) and this would mean that I am behind schedule due the 800 PV for week 1, but actually I am ahead of schedule. Ins this case would be better to compute EV as: If 60% is done then my EV is at least 800 because I did what was planned for week 1, plus i did a 10% of the remaining 50%, so i will have 20% of the 200 PV of week 2, obtaining an EV of 800 + (10%/50%)*200 =840, so now my EV would be bigger than PV for week 1 and I could see clearly than I am ahead of schedule.
Based on that, Am I thinking this right or the proportional thing is something we always have to assume.
Hope I made myself clear.
Thanks in advance.

You need to claim the proper % complete based on the way you developed the plan. For EV, we calculate the costs of the development of the project's product because EV is a COST control tool. It would be incorrect to simply spread those costs proportionally across the duration because your AC will not be proportional and then your CV would be unusable. While you can calculate SPI and SV with it, it is an unuseful schedule control tool. Use Earned Schedule for that.
But if your focus is the schedule (and assuming you'll calculate your schedule variances using earned schedule), you can build your planned schedule (PS, like PV) not only using dollars (like for EV) but also using days (duration) or physical completion.
When you claim earned schedule (like claiming earned value) you claim it using the same method you used to establish the planned schedule.
Take a look at the graph below. This represents a project where, depending if you are looking at days (straight line obviously), physical % complete, or costs, you get three different curves with three different % complete values despite being at the same place in the project. So if you used physical % to establish your PS, then you use physical % to claim your ES. The math does not care what you use. For the example below, 50% physical complete = 38% duration complete = 12% budget complete.
Just stay consistent.