By going larger, a better fast light cruiser is possible

Keeping in the Italian design mode (except for the British), I went to a larger design (something like the Duca d'Aosta). My design is underperforming because of the limitations of Springsharp. I cannot obtain light enough machinery to be equal the real world performance. My ship has 8-6in QF, 4-4in AA, and 16-40mm AA guns with 6-21in TT and a speed of 36 knots. My ship only has a belt of 2in and a deck of 1in. This is the Springsharp report:

GB/CL/1929, Great Britain Light Cruiser laid down 1929 (Engine 1950)

Displacement:
 8,057 t light; 8,325 t standard; 8,950 t normal; 9,450 t full load

Dimensions: Length overall / water x beam x draught
 613.45 ft / 608.00 ft x 56.00 ft x 21.00 ft (normal load)
 186.98 m / 185.32 m x 17.07 m  x 6.40 m

Armament:
      8 - 6.00" / 152 mm guns (4x2 guns), 108.00lbs / 48.99kg shells, 1929 Model
   Quick firing guns in turrets (on barbettes)
   on centreline ends, evenly spread, 2 raised mounts - superfiring
      4 - 4.00" / 102 mm guns in single mounts, 32.00lbs / 14.51kg shells, 1929 Model
   Anti-aircraft guns in deck mounts with hoists
   on side, all amidships
      16 - 1.57" / 40.0 mm guns (8x2 guns), 1.95lbs / 0.89kg shells, 1929 Model
   Anti-aircraft guns in deck mounts 
   on side, evenly spread, 6 raised mounts
 Weight of broadside 1,023 lbs / 464 kg
 Shells per gun, main battery: 150
 6 - 21.0" / 533.4 mm above water torpedoes

Armour:
   - Belts:  Width (max) Length (avg)  Height (avg)
 Main: 2.00" / 51 mm 470.00 ft / 143.26 m 12.00 ft / 3.66 m
 Ends: Unarmoured
   Main Belt covers 119 % of normal length

   - Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
 Main: 2.00" / 51 mm 1.00" / 25 mm  2.00" / 51 mm

   - Armour deck: 1.00" / 25 mm, Conning tower: 4.00" / 102 mm

Machinery:
 Oil fired boilers, steam turbines, 
 Geared drive, 4 shafts, 120,587 shp / 89,958 Kw = 36.00 kts
 Range 6,000nm at 15.00 kts
 Bunker at max displacement = 1,125 tons

Complement:
 459 - 598

Cost:
 £3.173 million / $12.693 million

Distribution of weights at normal displacement:
 Armament: 128 tons, 1.4 %
 Armour: 1,037 tons, 11.6 %
    - Belts: 454 tons, 5.1 %
    - Torpedo bulkhead: 0 tons, 0.0 %
    - Armament: 148 tons, 1.7 %
    - Armour Deck: 398 tons, 4.4 %
    - Conning Tower: 37 tons, 0.4 %
 Machinery: 2,885 tons, 32.2 %
 Hull, fittings & equipment: 4,007 tons, 44.8 %
 Fuel, ammunition & stores: 893 tons, 10.0 %
 Miscellaneous weights: 0 tons, 0.0 %

Overall survivability and seakeeping ability:
 Survivability (Non-critical penetrating hits needed to sink ship):
   9,182 lbs / 4,165 Kg = 85.0 x 6.0 " / 152 mm shells or 1.2 torpedoes
 Stability (Unstable if below 1.00): 1.16
 Metacentric height 2.8 ft / 0.8 m
 Roll period: 14.2 seconds
 Steadiness - As gun platform (Average = 50 %): 67 %
   - Recoil effect (Restricted arc if above 1.00): 0.44
 Seaboat quality  (Average = 1.00): 1.33

Hull form characteristics:
 Hull has rise forward of midbreak
 Block coefficient: 0.438
 Length to Beam Ratio: 10.86 : 1
 'Natural speed' for length: 24.66 kts
 Power going to wave formation at top speed: 58 %
 Trim (Max stability = 0, Max steadiness = 100): 50
 Bow angle (Positive = bow angles forward): 5.00 degrees
 Stern overhang: 3.00 ft / 0.91 m
 Freeboard (% = measuring location as a percentage of overall length):
    - Stem:  28.00 ft / 8.53 m
    - Forecastle (20 %): 25.00 ft / 7.62 m
    - Mid (67 %):  25.00 ft / 7.62 m (17.00 ft / 5.18 m aft of break)
    - Quarterdeck (15 %): 17.00 ft / 5.18 m
    - Stern:  17.00 ft / 5.18 m
    - Average freeboard: 22.60 ft / 6.89 m

Ship space, strength and comments:
 Space - Hull below water (magazines/engines, low = better): 115.8 %
  - Above water (accommodation/working, high = better): 178.7 %
 Waterplane Area: 21,513 Square feet or 1,999 Square metres
 Displacement factor (Displacement / loading): 114 %
 Structure weight / hull surface area: 98 lbs/sq ft or 479 Kg/sq metre
 Hull strength (Relative):
  - Cross-sectional: 0.91
  - Longitudinal: 2.21
  - Overall: 1.00
 Hull space for machinery, storage, compartmentation is cramped
 Room for accommodation and workspaces is excellent
 Good seaboat, rides out heavy weather easily