[ultra]

I'm not a tuner but I had a similar 'power ceiling' issue with my car in Dubai.

Long story short - getting past 180whp turned out to be a matter of going for a full, proper exhaust (headers + overpipe + front pipe + mid pipe + back box).

I've had 3 exhaust combos on my car (bit of a hodge podge, sorry):

Combination 1:
Stock headers, overpipe & front pipe + Remus mid pipe & back box
= 181.5 whp

Combination 2:
JDL UEL header + stock overpipe & front pipe + Blitz NurSpec C-TI mid pipe & back box
= 175 whp

Combination 3:
JDL UEL header + JDL Overpipe + HKS Hi Power (catted) front pipe, mid pipe & back box
= 189.9whp.

PS - Panel filter only; AFRs tapering down to 12.7 ish at redline IIRC (opted for a safe-ish, richer tune)

TL;DR Go for a full exhaust man & good luck with your tuning!