YES! The last 6 month T-bill had a cut-off yield of 4.00%, meaning partial allocation at 4.00% and a full allocation at 3.99% (or 3.85%). Big difference. The next T-bill could have a cut-off yield of 3.92% (for example). These particular 15 basis points matter a lot
within the current bidding environment. They can easily mean getting a T-bill (at a still acceptable price for SA shielding) or not.
A 3.95% COY 6 month T-bill, for example, beats any bond unit trust-based shielding method. But if you didn't do your financial math reasonably accurately you wouldn't know that, and you'd avoid sub-4.00% COY T-bills. But we should know better: convert EIRs to COYs so you bid reasonably well.
When T-bill COYs fall below 3% (for example) none of this will matter. But these 15 basis points, right now? Huge for bidding intelligence.
how much do normal people shield? 200k? 0.15% for 6 months the difference $150. is that a lot of money for 6 months? we are not dealing with millions and millions. i say again it is not significant.
See above.
Let say I have invested all my OA funds in T-bills and intend to do SA shielding, I would have only 20k and 40k left in both OA and SA account respectively. At 55 yo, will the balance go into my RA?
Yes, in your example your RA would be funded at $60K on your 55th birthday: $40K from SA and $20K from OA. (In practice it wouldn't be
exactly that because T-bills are in $1,000 face value increments, but you've got the basic idea.)
Do I need to top up using cash if I want FRS?
Maybe. You may have a couple other choices:
1. If you have a spouse then he/she can (usually) transfer his/her OA dollars into your new RA.
2. You can keep your SA shield in place, wait for your T-bill(s) to mature, transfer OA dollars to RA, then finally release your SA shield. This doesn't really work with the unit trust-based SA shielding method since you usually wouldn't want to wait that long, but it may work if your SA dollars are invested in a T-bill that has an acceptable yield and that matures after your OA-purchased T-bill(s) do(es).