"Everybody else in the top 10 upwards - Blackpool, Barnsley, Huddersfield - they were all expected in the play-offs," Wellens added.
"Reading are a massive club. Everyone goes on about the problems that Reading have got. The wage bill is double ours, they have got a Cat 1 academy, which all the players come from.
"And then the top four are huge compared to us."
The top of League One was the least of Orient's concerns in August as they began the season with four straight defeats to leave them propping up the table.
At that stage, "everyone is going 'there's a chance of relegation,'" Wellens said.
It was not until December that Orient began the two-month, 11-game unbeaten run that saw them surge away from trouble and propelled them up the table into promotion contention.
After that impressive spell of form was ended by a home defeat to Stockport on February 1, Orient reeled off three more successive victories.
The last of those was the win at Wrexham that left Wellens dreaming before injuries to Omar Beckles, Jack Simpson and Dan Happe plus Jack Currie's suspension left Orient down to the bare bones defensively as they suffered five straight and damaging defeats.
The 2-1 home loss to Charlton in the middle of that run, following two late goals from the Addicks, was described as a "sucker punch" by Wellens.
League One's 21-goal top scorer Charlie Kelman
Orient recovered impressively once their missing men began to return, losing just one of their final 10 games, winning eight of them, to secure their place in the play-offs and head into them with real momentum.
Wellens cited the improvement of youngsters such as the loan trio of goalkeeper Josh Keeley, attacking midfielder Jamie Donley (both from Tottenham Hotspur) and left-back Currie (from Oxford United) plus midfielder Jordan Brown and winger Ollie O'Neil as important during the course of the season.
Donley topped the League One chart for assists, setting up 10 goals, and also scored eight times in the league.
The mid-season window was key for Wellens too when he was able to bolster his squad with the additions of free agent Randell Williams and fellow winger Dilan Markanday, on loan from Blackburn Rovers, who both featured regularly in the second half of the campaign.
Striker Charlie Kelman's efforts have also been vital, his 21 strikes seeing him finish the season as League One's top scorer.
"We've got a culture and environment where people come and flourish," Wellens said.
"Our supporters are brilliant, our chairman [Nigel Travis] is important in that because the way he runs the club drips down to everybody and makes everybody enjoy it."
Manchester-born Wellens now wants that enjoyment to continue into the play-offs.
He said: "It [Stockport] a nice local one for me. It's probably it's probably the nearest club to my house in Manchester apart from Manchester United.
"Let's just enjoy it. Full house at their place, full house at our place. Let's give it everything we have got. We've got nothing to lose."
