There is no GFA limit for landed properties, which is limited by the envelope boundaries.
However, the original developer that sub divided the area into multiple plots have to pay Development Charges to enhance the land from the original baseline GFA to the proposed GFA. DC rates are typically half the market land psf, not a small sum.
As such, the original developer will not attempt to build to the max envelope, since the selling price for landed is typically based on land psf.