Ghaziabad's super area calculations are misleading

My current 2BHK in Sector 6 was 1200 sqft super area, but carpet area was barely 800. Now I'm looking for a 3BHK, maybe in Raj Nagar Extension, and builders like SB Group are quoting super areas that seem way too inflated for the actual usable space. Matlab, 1800 sqft super area for a 3BHK, but carpet area kitna hoga? I'm trying to upgrade, not just pay for common areas. Is there a thumb rule for super area to carpet area ratio in Ghaziabad projects? I'm worried about paying a premium for unusable space. Also, are floor-rise premiums actually worth it if you're already paying for a high super area? It feels like double charging. Any tips on how to negotiate this super area trap? Already have a home loan, so every rupee counts. Hope someone has cracked this.