Last month, the city’s planning board delayed a decision on zoning and land-use changes for the Brickell Flatiron swap, in part because some members thought the city should extract more land from developers than it is giving up. The majority also felt uncertain about what Kauderer was offering because he has not yet submitted plans for his new building.

Sarnoff, who has been a key player in both park deals along with city planners, said he has pushed to expand the size of the developers’ initial land trades. For instance, he said, the park initially proposed by Related was much smaller. Now the city will get about an acre of tree-shaded park, including a sculpture garden, an exercise course and a dog run.

“I joke that it started as a postage stamp and it became an acre,” said Sarnoff, whose district includes Edgewater and Brickell. “It was a good quid pro quo.”

Sarnoff estimates both deals will produce a bit over three acres of park which would have cost the city a few million dollars. He hopes to do the same as other projects come up, and says the template might prove useful in other city districts.

Related’s “high-end luxury” tower, at 43 stories, a long, thin tower designed by Arquitectonica with a façade of rippling balconies, would parallel the shoreline. Its south end would be raised 25 feet off the ground on columns, affording an expansive view of the bay from 28th Street.

The landscaped park would wind under and around that southern end and extend onto an adjacent lot owned by Related.

The Crimson developer would provide a public pedestrian path along that condo property’s western edge so that residents of 27th Street to the south can walk directly into the park. Crimson’s developer, meanwhile, is asking the city to vacate an “alley” that, on paper at least, runs along the northwest corner seawall of the property. The alley doesn’t actually exist, and a chunk of it lies under water in the inlet.

Related would add a new street between the buildings to 29th Street, connecting the two streets for the first time.

The Brickell Flatiron has been through two designs that followed the lot’s triangle shape, including a city-approved 80-story tower by famed architect Enrique Norten that Kauderer said was scrapped after the real-estate collapse.

Kauderer’s revised plan would require taking over the portion of the city’s Allen Morris park that abuts his property. The park, donated to the city by the real-estate developer, is split in two pieces straddling Tenth Street.

With that additional sliver, Kauderer said, he would have a squared-off, more-efficient lot to build on, allowing him to drastically reduce the size of what would be a 16-story parking garage at the tower’s base. He would put an open plaza on some of the park site and would save its big oaks, Kauderer said.

“It provides us with a nicer project,” he said.