Thats always been my experience too. Max reps never seems to go up, but anything sub-max gets easier. Strange!
Exactly Rik. I actually have a little auto regulation built in. If it gets harder towards the end of the week, then I'm doing a little too much and I'll either cut it back a rep or leave it there for another week. If I get a consistant week where it seems a little easier at the end of the week, I'll look at adding a rep for the next week. I'm in no hurry. I know this will get me where I want, my only concern is if I will hit my stated goal by the end of Feb or not.
At least i'm not alone. I'll have to figure whats going on here. Maybe it's body weight related, I'm going to keep track of my weight for sure. I know it tends to fluctuate quite a bit.
Maybe we both fail because of the same body part. Possibly Biceps letting me down, as I dont really train to increase my curls much. It's hard to figure out exactly which part is failing when I get to the last rep, too busy trying to stop my eyeballs popping out to notice
On most lifts we'd break up the load-volume scheme. It's harder to do with pullups, especially if we're still at low reps. That's why I think Ferruggia's ideas about doing multiple singles, doubles or triples is valuable. Ladders similar. If you're stuck on your dead or squat, you'd probably drop the weight and do some high-rep work for a while, then shift back to heavy, low-rep stuff. Not convenient to do with chins the way most of us do them.
On the other hand, somebody that's doing 21 chins will probably benefit more from adding weight for a while.