liquidity

you enter into a payer swaption to pay fixed.
you would enter into it if the price of the fixed portion is < Strike Price.

If you are thinking in terms of Put or Call options on a bond -- The fixed price would fall below the strike price for a bond when the Interest rate rises - and you have the option to then PUT the bond back.

(P)ayer Swaption=(P)ut option on BOND

So Re(C)eiver Swaption - likewise would be (C)all option on Bond.

CP