You could try making it run a bit leaner and see if you can get a few more ponies from that. The OFH ignition advance is already pretty aggressive, though you could try adding ignition advance incrementally where there is no knock corrections.
The tire size you inputted will have an effect on the Vdyno calculations and total weight to a lesser extent. The numbers might be slightly off between different wheel/tire setups, so that might have thrown your numbers off a little. Though 174Hp with a stg1 tune and stock header is pretty impressive. It's quite possible that the stg.1 pull you did was reading high. Good luck.
For your reference, my stg 1 tune got me about 165-168hp on 91 fuel. Stg 2 with Tomei EL my pulls were getting between 178-181hp pretty consistently.