The Australian spent five seasons with Ducati, initially with Pramac between 2018 and 2020, before stepping up to its factory squad in 2021.
The four-time race winner has switched to KTM for 2023 and enjoyed a strong debut at the Portuguese Grand Prix, finishing fourth in the sprint and seventh in the main race.
Comparing the RC16 to the Desmosedici he previously rode and which won both races in Portugal, Miller said: "To be honest I felt it was less than the Ducati in terms of physicality.
"The bike itself is rather nimble. My neck was a bit stiff towards the end, but it always gets pretty stiff here in Portimao.
"You've got three rights in a row at the first corners, so the time you switch over for the next corner you're trying to stretch it."
KTM's pre-season wasn't straightforward and the team appeared to be on the back foot coming into the first round of the season.
But both factory riders making it into the top seven in the main race, as well as Miller ending Friday fastest and qualifying fifth showed the KTM is in a better position than originally thought.
Jack Miller, Red Bull KTM Factory Racing
Photo by: Gold and Goose / Motorsport Images
How close to the frontrunners it is will not become apparent until after the next few rounds, given the Portuguese GP followed two days of testing at the Algarve venue.
But Miller believes that all the work KTM has done in refining the set-up of the RC16 in Portugal will pay dividends in the coming rounds.
"I feel like the steps we've made in terms of electronics and strategy and that kind of thing, in terms of set-up our plan coming into this grand prix was to not turn the bike upside down anymore," Miller added.
"We'd been doing that, and we kind of got comfortable on the last day [of testing].
"Our main plan for this grand prix was just normal race weekend stuff, let's play with settings, let's get the bike in a decent position and work on myself riding the bike. And I think we've been able to do that.
"Cross my fingers, we won't know till we get there, but I really do think that the strategy we've got now, the way we've got the electronics in place, the way the chassis is working, we can make it work at these upcoming events."Read Also:RNF calls for harsher MotoGP penalties after “reckless” Marquez crashMarquez won't escape Oliveira MotoGP penalty despite Argentina absenceBezzecchi doesn't expect consistent repeats of Portugal MotoGP podium in 2023 2023-03-28T16:59:48Z dg43tfdfdgfd