Unlike the previous example of Solar and Stalker, Riposte and Arquero have slightly varying ranges for their Super Duo bonus. This means that Riposte can be utilised slightly further forward to achieve Arquero's bonus as he hangs back, but would not benefit herself.
However with these two it is not just about the simple Trait bonus. There are other synergies available also.
Consider using Fatal Flaw* and Strike against a target that Riposte is in Base to base with. the typical order of play would be Fatal Flaw* then Strike. However, if say using a Resource such as Heroic Surge: Battlefield Control, you could use the Strike first for possibly some Damage, follow up with combined Fatal Flaw* then Activate Arquero to make use of either Arcing Fire or Rain of Arrows targeting the same model Riposte is engaged with. The advantage here being that Arquero can Power-Up his combat Action, so benefiting from +3 from Fatal Flaw* (if successful) and the Power-Up die to maximise Damage output, to a potential result of 16 in contrast to Riposte's potential result of 13; assuming some Damage is inflicted, that is +1-3 extra Damage. Even if using Rain of Arrows and risking catching Riposte, she should be at an increased Agility so lessening the chance of Damage. This can work with many other models besides Arquero, it is just that in tandem even the riskier Rain of Arrows option improves the odds for Riposte.