You need to focus on spread income, which is mostly the 10-year number. The 'cost' of borrowing is the short term rates which can be as high as the 2-year but generally has been 1-6 month rates.
This is why a spike in the short-term rates would be bad for the companies if it were not also accompanied by a spike in the longer term rates. This means you want a sharper curve, not a flatter curve in the treasuries.
In terms of interest income on newly purchased MBS, yes.
But asset value goes down along with the treasury market.
If it continues what will happen is that book value will drop below market price for the stock, and we'll start having accretive offerings again. And that tends to moderate off-cycle purchases of the stock, which keeps price from appreciating. Not that it's been doing any appreciating while the SPOs are suspended...