I'm on page one but I already agree, it's about being in readiness. If I'm in the middle of something and he interrupts me then I feel very irritable and I'm liable to snap at him. He hates that. So when he's at home, a large part of my effort goes towards keeping myself in a mindset of readiness to drop whatever I'm doing and interact with him.
It's partly that most of what I'm doing when I'm active at home is not super fun stuff. It's chores, cleaning, folding laundry etc, and if I'm alone then my attention is taken up with constantly evaluating how to get it done more efficiently so I can eke out some downtime at the end of the day, or even just get it all done before bedtime. So if he tries to talk to me when I'm folding laundry or running up to the upstairs bathroom to spray it with disinfectant, then it ruins my whole plan, because I forget the choreography that will allow me to get everything done in an efficient way. Then everything takes twice as long because if he distracts me with some news story or something, then I forget to put down the disinfectant in the bath until it's too late, which means I can't actually clean it today, because I won't have time to finish before I need to get the kids from school. That means I need to leave it till tomorrow, which means that I won't be able to do [fun thing] that I was hoping to do tomorrow because I'll be cleaning the bathtub. So although he doesn't understand why I get frustrated when he interrupts me, there is actually a reason behind it.
But my marriage needs me to not behave irritated when my husband talks to me so when he's at home I tend to use up a lot of my mental effort on being ready to respond politely if he wants to talk about the news or go for a walk or eat lunch together etcetera. And it doesn't leave a lot for getting housework done efficiently.
When I realised this was the cause of why I wasn't efficient when he was home, it actually helped a lot because I made sure to keep some chores in reserve that "don't mind" being done in bits and pieces. Wiping out dirt from kitchen cupboards, cleaning microwaves, and that sort of thing. So if he starts talking to me I'll clean the microwave while he talks, or sort a kitchen drawer, or clean a cupboard door or something, and then it's off my to-do list for later.
But I also generally lowered my standards a bit, as there isn't a perfect way to remediate the loss of efficiency of trying to get chores done when your mind is not really on your work. Things really are more efficient if, while you're going up the stairs, you're thinking, 'Ok, spray bathtub, bring down delicate laundry, take bedclothes off son's bed. Next trip, bring soap refills upstairs, take old bedclothes downstairs, get them into the wash before noon.' Once you lose that thought, it's never coming back in its fullness, if you know what I mean.