If you find yourself trying to "grab a punch" to do an Aikido technique, what you are doing is playing the other guy's game.
You need to either ignore his game - just go in there and take him down - or else get him to play your game, which you might be able to accomplish by fooling him into thinking you are closer than you are, or fooling him into thinking he can take you out with one punch.
My thoughts on how this relates to the OODA loop is that you either want him to Orient himself improperly so that he makes a poor Decision and thus you can Act before he does, or you want to move in after he has Decided but before he has Acted.
YMMV. You need to play around with people with different skill sets to learn how different people behave.
Was about to type a bunch of stuff, but instead I'll just say ... What he said up above.