Depending on hedging, the impact can be much bigger than just the extra 2 hours in the current situation. Take a simple example. A long-haul widebody burns about 6 tons of fuel per hour. A normal 9-hour Europe–India flight burns about 54 tons (9 × 6). If rerouting adds 2 hours, total burn becomes 66 tons (11 × 6). That’s 12 extra tons, or roughly +22% more fuel. Now assume fuel just increases about +20% increase in price. If an airline is unhedged, both effects hit at the same time: +22% more fuel burned and +20% higher fuel price.
Total fuel cost per flight becomes roughly 1.22 × 1.20 = 1.46, so about +45–50% higher than before.

If the airline is fully hedged at the old price, then only the +22% volume increase applies. So while the route is only about 20% longer, the fuel bill can easily jump close to 50% in an unhedged scenario.
Hope I did the math roughly right (i know it is simplified)

PS: For LH "Up to 4% of exposure is hedged monthly for up to 24 months" - Not sure about the current numbers: With an 85% hedge ratio, a 20% fuel price spike does not translate into a 20% higher fuel bill. The immediate impact would be much smaller, unless disruptions materially change planned fuel consumption or persist long enough to roll into less-hedged future periods. If fuel price rises +20%, only 15% of the fuel volume is exposed, effective price increase on total fuel bill ≈ 0.15 × 20% = approx 3% impact (ignoring basis differences and option costs).