Developers anticipate a slight delay in filing plans for their large Mattapan Square mixed-use project in the wake of a community meeting on Tuesday night that was so consumed by a discussion about unit affordability that no time was left for a review of the development’s design.

Nuestra Comunidad Development Corporation and the Preservation of Affordable Housing Inc. (POAH) held their fifth informational meeting about their proposal to re-use what is now an underused MBTA-owned parking lot next to the trolley and bus station on River Street. The meeting, held in the Mattapan library on Blue Hill Avenue, drew about 40 people.

The non-profit groups submitted a winning proposal to re-develop the parking lot in 2016, proposing a mix of affordable and market rate rental units and 10,000 square feet of new commercial space they hope will heighten activity in the increasingly transit-rich neighborhood.

Along with 135 units of housing, the most recent plan includes 173 parking spaces for an overall parking to unit ratio of 0.5, including MBTA-required station-specific and on-street parking. The property sits behind the Mattapan terminus of the Red Line’s high-speed trolley extension, not far from the site of the future Blue Hill Avenue station on the Fairmount Line and adjacent to the newly completed leg of the Neponset River Greenway.

The Nuestra-POAH proposal, which beat out a second proposal for the lot put forth by Trinity Financial, Inc., included payments in excess of $4.8 million over the next 20 years for the lease they will get from the MBTA.

Speaking to the Reporter after the evening meeting, David Price, executive director of Nuestra Comunidad, said that the session largely ended up as an explainer for the 30 to 40 attendees on the mechanics of affordable housing. “We want to be transparent about what the needs are,” Price said, adding that the meeting was held in response to community feedback about the unit prices.

The city requires that larger developments dedicate at least 15 percent of on-site units to affordable housing, or 18 percent off-site. POAH-Nuestra has indicated that 50 percent of the units in this project will be affordable.

Although the bar for apartments available for Low Income Housing Tax Credit is 60 percent Area Median Income (AMI), POAH-Nuestra is trying to set as many of those units as possible at 50 percent AMI. For a family of four, that would top out at an annual salary of $51,700, “a really good work force number,” Price said.

By designating some of the housing at a lower 30 percent AMI level, as well as meeting a city standard for units made available for those in danger of homelessness, the developers expect a solid blend with the apartments slated for a higher market-rate income bracket.

“We think the mix of incomes is a good thing,” Price said. “It’s a good balance between affordable and market rate.”

The team anticipates another meeting in about two weeks that will focus on the overall design, Price said.

Given that there could be tweaks to the design before that session, POAH-Nuestra is not publicly airing the planned presentation, but Nuestra Comunidad officials said there are no significant changes.

They plan to file with the Boston Planning and Development Agency in August to begin the Article 80 Large Project Review process after the design meeting. This will set off a series of city-led community meetings and include a detailed filing on the project plans for residents to review.

“In the scheme of things, it’s not a big delay at all,” Price said.