When ironman was introduced here were the comments
“Plus, exclusive to Horde, Ironman adds a 5% XP bonus for all XP earned and XP Bounties completed during the match.”
The Horde results page does not match that statement.
Actual ironman xp bonus is
Wave Completion 2.5%
Ribbons 2.5%
Consecutive Wave Bonus 2.5%
Bounty Bonus 5.0%
Since bounty bonuses are not impacted by xp bonus events, I wonder if the 2x xp change is driving the 2.5 result. which means if there was a 4x xp event the ironman bonus would be 1,25%.