You may not have, but the origin of this discussion is Mountain Explorer's comment that the difference in UA's J cabin size is larger in terms of seat count simply because of the higher density configuration, meaning that you can fit more Polaris seats in the same amount of space as a certain number of D1 seats. That very clearly implies there is a quota / fixed allocation of floor space to a J cabin that DL is fitting fewer D1 suites into and UA is fitting more Polaris seats into, which we both agree is absolutely not true (and as I have repeatedly pointed out with higher-J configurations vs average configurations vs. leisure configurations). I believe the exact term you used was "not reasonable" which is not exactly "not feasible" and that's totally fair (and I started with "not reasonable" earlier in my previous comment as well), but the exact same comment still applies if you substitute in "not reasonable" with in place of where I used "not feasible." Why is it not reasonable to go over 40J? Because it's not enough space for the other cabins? Maybe for DL given DL's hubs, route network, traffic mix, revenue maximization strategy, etc. and how those factors (as well as potentially others) differ from UA and other airlines. However, the conversation hasn't really delved into much of that up to now and the statement of "expanding the J cabin any more than 40 seats on the A359 is not reasonable as it will eat into the space needed for other cabins" without additional detail on WHY that additional space for PE/Y+/Y is needed relative to other carriers (either in the same country (UA) or flying the same J seat that takes up the same amount of space per seat (QF) is not really a complete answer to the questions and discussion further upthread (such as PA815's about why UA's 787-9 has more J in a regular config than DL has on a larger A350 with a high-J config). Is it the hubs and the amount of business / high end leisure O&D demand and / or suitability for certain connecting traffic flows? Is it the routes flown from those hubs? Is it the differing revenue maximization strategies as RaflW pointed out? Is it the difference in "seat density" between D1 and Polaris as Mountain Explorer posed and I did the "basic math" for? (hint: it's not sufficient to be the primary let alone exclusive reason that Mountain Explorer makes it out to be) Is it higher average J fares from offering a less dense seat that J customers are willing to pay more for (doubtful based on fares on directly competing routes but possibly)? Is it something else that has not been mentioned yet? That's what I'm interested in learning about and discussing (as it seems others are) vs just leaving it at "they're different airlines with different needs"