No, in this case your OA is partially “shielded.”
That’s not necessarily a bad thing since even 2.5% interest is pretty good these days. So what you might do is shield SA, keep your OA shield intact, and then top up your RA when it’s formed — up as high as the Enhanced Retirement Sum if you want. Or if you want to return some CPF Investment Scheme (OA) investments back to OA just before your RA is formed in order to fund your RA that way, that works.
Another possible approach is to release all your CPF Investment Scheme (OA) counters back to OA, raise a SA shield, let your RA get well funded primarily from OA, withdraw OA, reinvest those OA dollars in a lower cost way than the CPF Investment Scheme, and even add some dollars to your RA. The idea here is that the CPF Investment Scheme (OA) is generally quite an expensive way to invest due to the endless fees and high commissions, so even if you want to maintain those investments (or similar) you might decide to exit to greener, lower cost pastures. This’ll depend to some extent on whether you still have compulsory contributions coming into CPF and whether you’ll keep those funds in the traditional accounts.
Slightly complicated, isn’t it?

You have quite a bit of flexibility in how you can handle your RA creation and funding.