Well most of the true experience of what you perceive is related to what frequency response you are receiving at your eardrum combined with any recent comparisons (psychological burn-in you have with other differently toned headphones or speakers) you've made recently. The first point about what frequency response you're receiving at your eardrum - closed back headphones can often be quite finicky about how much bass you get, determined by how good you have seated your headphone for that listening session - some are more sensitive than others - for instance I know that my NAD HP50 closed back is extremely sensitive to seating position when it comes to bass perception & I've validated that unreliability through measurements of that headphone on my miniDSP EARS - it's very variable in comparison to my other headphones in the bass, and I had to do quite a few failed measurements (which I threw out) to even get the following kind of inconsistent consistency from pthe HP50 (and compared against the easy to measure/ easy to wear "chuck it on" K702):
HP50:
View attachment 200141
K702:
View attachment 200140
So it's possible you're getting a different experience in the bass with each headphone seating - you'll have to experiment with that.
The other variable is that you can't always guarantee what your actual bass frequency response actually is even when you have a good seal if you haven't had your individual headphone unit measured - I've found that since I've had the miniDSP EARS and have done EQ's based on the measurements of my actual units that the bass is noticeably more reliable when listening - because I'm crafting the shape of the bass from 200Hz down to 20Hz with good precision for my unit of headphone.
The elements of "slam" and such like are all explained by the frequency response of the headphone, if you can control it or conversely play with EQ a little to enhance it then that is where you will end up at. In my experience you can get adequate slam from a headphone following the Harman Curve in the bass, as long as it is really following that curve based on your headphone's unit to unit variation & how it seals on your head. The easy option is to place a Low Shelf Filter of Q0.71 at 105Hz and increase that until you have enough bass which should hopefully introduce some "slam" back into it - however I think the shape of the bass from 200Hz down to 20Hz will dictate your slam, and it's harder to get a clear picture on what's really going on if you haven't measured your individual unit or if you suspect you have seal issues when wearing it. I don't wish to put doubt in your mind about "knowing" what your headphones are doing on your head, but headphones can be a real bitch to know what's going on with them, it's a bit of a rabbit hole, the more you know the more you realise the ways in which they can be innacurate!
EDIT: regardless of what I've said, it's true that any given headphone & EQ will sound it's best at a certain "arbitary" volume level, and I normally tweak the dial to get it sound the best for any given track as long as it's not too loud.
EDIT #2: what most users can do to minimise these problems is to choose headphones with historical low unit to unit variation combined with headphones that are known to seal well to most users (this way you can guarantee with greater certainty that any EQ's you find on the net are more relevant to your unit & yourself, they will be more accurate) - that's how you mitigate those problems and get the best experience if you're not in a position to measure your unit yourself.