Often use thirds and two-thirds for window sizing. The current thirds and two-thirds window sizing extend to the edges of the screen. Will thirds and two-thirds have a Sequoia like gap or do you know the gap sizing so that it can be mimicked with a custom move/resize?
BTT does have an option to add margin around, but it's a bit different than Sequoias default:
Currently the easiest to replicate the Sequoia margin would be by creating custom snap areas:
Of course you can also disable the Sequoia margin if you just want to have everything the same (that can be done in System Settings => Desktop & Dock => Tiled Windows have margins