Shout loud enough and long enough and one of us'll show up, eventually...
The reason we (Shanwick) ask for the MAX on the ORCA/ACARS or VHF/HF requests is that we, and those "customers" who are happy for us to adopt this procedure, would prefer to clear you 1 or 2k above your requested level rather than dump you 3-5k below should your requested level be occupied. The alternative being you're stuck down in the weeds with no chance of higher on a busy track from OCA entry all the way to landfall.
The work load issues for us were such that dumping flights only to then have them come up on VHF/HF to say they would prefer +1000' to -3000' meant that we adopted this procedure to try and get ahead of the game. We know those driving a 777 or 330 can get to the parts that the 767 ot 747 boys can't reach, therefore even if no MAX appears on the clearance we will, if needed, make an educated guess and, for example, bump the A330 out of EDDF up to 370 despite the request only showing us the requested level of 360.
Correct me if I'm wrong, but would you prefer 370 coast to coast having requested 360, or 320 with no chance of higher until Gander get you under radar some 3.5 hours later?
All we can do is operate on a first come first served basis and for everyone who can't get what they want, 'cause somebody else got there first, spread the pain as evenly as we can. As had been said previously, we don't ask if we've no good reason and we're trying to provide a service to you ALL.
We're also aware of the factors that come into play and many of us, self included, have sat up front traversing the pond on more than one occasion and been happy to chat about the 'bigger picture', from both sides. We also realise that you guys can and will go that bit extra under certain circumstances; we've all asked if somebody can take higher to help traffic below and been told negative, only to have a different reply when it is pointed out that it is company traffic which is below.
If you ever get a stop in EGPF/PH/PK then come see us; it's worth it for the cooked breakfast if nothing else.
PS I was working early hours this a.m and had to deal with the c@@p south of the Shannon FIR. I felt most sorry for an AFR who I had to dump from 340 to 290 due traffic above wanting lower, only for everybody to get bounced around at every level between 270 and 370. AFR eventually got 380 once everybody above was out the way, but rest assured we understand how frustrated you can get being moved around and all the while being stuck in the you know what.