Perez says Force India's own calculations have pointed towards Lotus's E23 Hybrid having an outright performance edge on their VJM08 - at least before the wide-ranging upgrades his team introduced at Silverstone.
"I am surprised, because when we see all the simulations they seem to be half a second a lap quicker than us - but for some reason, some reliability issues, they haven't been able to exploit their full potential," commented the Mexican.
Lotus suffered a double retirement in Silverstone, and as a result lie sixth in the current standings on 29 points, 10 behind Force India. Nevertheless, Perez is certain his team's Enstone rivals - along with Toro Rosso - will prove their most serious competition in the battle for fifth overall.
"I think they're a big threat," he continued. "And Toro Rosso obviously have a mega car, [so] they are the two main ones. With people bringing upgrades every race, it really depends when you look, but Lotus and Toro Rosso should be our target to beat."
Perez stressed, however, that Force India aren't simply looking over their shoulders - and that they will do their utmost to overhaul fourth-placed Red Bull if the revisions to their car prove a success over the coming races.
"I think Red Bull should still be our target, to try and chase them in the points," he said. "If the upgrade goes well, then we should definitely aim for them.
"Basically our limitations have been the rear end of the car, in the quick corners. We expect to improve that, improve the entry - and improving that means everything comes together.
"You have more harmony with the car, and can extract the best out of it more easily. If we can have a bit better pace, that will come together with better tyre degradation and so on.
"There are plenty of things to look forward to: with an upgrade you don't just improve lap time, you improve so many things that have a benefit over a race weekend."
With nine rounds of the season complete, Perez's best 2015 result to date has been seventh place in Monaco. He has scored points on four other occasions and sits 12th in the driver standings.