I don't understand? What you are saying seems contradictory....
If you assumed a maximum of 3 X 2.5s why didn't you make the line boxes able to take them without modification? We assumed two out of each end so a total of 4. The size of the opening is dictated by IP2X requirements. So making a larger diameter would not work and changing the shape would have messed with the IP67 option.
Also, whoever mentioned 32A lever connections? The maximum current when using 2.5mm with lever connectors is 26A not 32A, says so on the connectors themselves if you look closely enough. Please see the next post (yellowvanman) post where I will ask a question about this - But I admit that I had assumed a ring, though with hindsight only one spur is allowed per point so it could not have been.
The nature of my installation was that I was splitting a radial into 3, and I wanted 1 cable going in and 3 coming out. I agree that sometimes if one of the cables comes from one direction and the other three go off in another direction it can look neater if one comes in one end and three go out the other. The "other box" would have all 4 coming out of one end. LINE two out of each end or LINE modified one out one end and three out of the other end.
I have not finished as yet, and might yet return to using adapted Line Boxes. Just wish they did not need to be reamed beforehand understood. It's a bit more effort but if you have the length of cables you can just insert 2, sandwich the third between and pull through.