It does not matter that your bike is less compact with a longer seatpost, you can not ride with a seatpost that is too short.
The Brompton solved this by making a telescopic seatpost
https://www.sjscycles.co.uk/seat-pos...c-seat-pillar/
I bought two used Bromptons for me and my son some years ago. We both have long legs and decided to take the seatposts that came with the bikes and make them into telescopic seatpost. They are made of steel so they have thinner walls than aluminium seatposts. Therefor it was possible to fit another shorter seatpost innside.