I consider myself to be a wimp because I compare myself to real painslut masos like yourself so my "teaching" you things in this area is pretty laughable. However, as we all know, I always have an opinion that I can't help but share and because I hate pain but do take it to please a Domme, I think I do have some insights in this.

My experience is that I can take a lot more with some Dommes than I can with others and I can take a lot more on my upper back than I can on my ass (meaning, in comparison with other subs). A lot of that difference is really because of the Domme and her techniques rather than me doing anything different.

Proper warmup and pausing by the Domme that allow the release of endorphins to actually take effect near the beginning (as well as teasing & rubbing the reddened skin during this pause) really makes a huge difference for when the Domme gets to the meat of the whipping/spanking. Obviously, this is totally outside of my control but when a Domme uses that kind of technique, I tend to slide into subspace really hard. The combination of the release of natural pain suppressors with the floatyness/separation of subspace really makes a difference in how much I can take. Also, the Domme communicating and instructing me to breathe, or to "take it for Me", or even to coach me through it are a big help for me.

Another factor is whether the strikes are rhythmic or random. If the strikes are rhythmic, it is much easier for me to cycle through the natural pain clench after one stroke and into muscle relaxation before the next one. However, a Domme who intentionally messes with me by faking strikes or being random may get more sadistic joy from the beating than something more rhythmic, but it does have a negative effect on how many strokes I can take.

Finally if we are counting strokes as the measure of the beating, then the implement and the impact zone also makes a huge difference. The third stroke on the exact same spot is going to elicit much more pain than 3 stripes... as does the time between hitting the same spot again. 10 strokes from a severe cane is easily overwheming whereas 10 strokes of a flogger is usually just a beginning.

My point being that pain builds on pain and too much unspaced and severe pain is what generally makes someone quit much faster than if the Domme is able to keep it from reaching that quitting stage through various techniques they employ. So, I don't know if your pain tolerance is actually dropping off or if it is just that particular beating that is making you reach it much quicker than others. You are the only person who knows if you are actually tapping out after feeling less pain or not regardless of the length of the beating itself.

As for my own techniques during a beating, obviously trying to focus on relaxing and even using self-hypnosis so as not to clench muscles or flinch before the strike hits really helps to absorb it (but also brings less pain from that strike). Breathing techniques that are similar to Lamaze and/or timing an exhalation to the strike (rather than the natural tendency to inhale, which tightens muscles) are also things I try to remember to use while "under the lash"... But, I admit that I tend to forget these things while trying to deal with the pain (which is why the Domme's words can have a big effect).

Not sure if this was helpful, but I hope it allows you to take more & to enjoy what you receive in a particular session rather than comparing your "performance" in one session to another.