Frame design models: make your choice
Horizontal top tube
Seat stays are welded  near the seat tube-top tube zone.
Horizontal top tube
Seat stays are welded 5-8 centimeters down the weld of top-seat tube
Top tube is slooping.
Seat stays near the top-seat weld tubes zone.
Top tube is slooping.
Seat stays are welded 3-5 centimeters down the top-seat weld tubes zone
Top tube is slooping.
Seat stays welded 3-5 centimeters up to the top-seat weld tubes zone.
Top tube is horizontal.
Seat tube has aero shape profile (only aluminum).
Seat stays are aero profile too, and welded 3-5 centimeters down the top-seat weld tubes zone for more aerodinamics.
Here you can choice your prefers tubes shape profile!