According to the link below the Helix's headphone output is 12 Ohms.
4 Best Headphones for Helix – Music Gear Zone
If that rating of 12 Ohms is accurate for the Helix's headphone output that means, using the 8:1 rule's recommended ratio, a headphone with an impedance of around 96 ohms should be well matched to the Helix. You can of course go higher(or lower) but the more the headphone's impedance exceeds that 96 Ohm mark, the more you may have to turn up the headphone volume. As you up the impedance rating of the headphones there can be a point of diminishing returns, where you feel as if you are not able to get adequate headphone volume anymore. This will depend to some extent on the construction and sensitivity/efficiency of the headphones.
Headphones Ohms Ratings Explained - zZounds Music Blog
Update: I always try to use the equipment I will be using on stage to design presets intended for stage. I use an FRFR primarily as a monitor as it is most similar to a PA speaker. Stands to reason the results are just more predictable. If you do use headphones though, it occurs to me that in addition to the quality and inherent frequency response characteristics of a given headphone, that impedance mismatches may contribute to why some users get worse results than others when taking those presets, designed with headphones, directly to stage(usually a bad idea anyway IMHO). The Fletcher Munson Curve, as usual, is probably a big factor in this as well. See the quote below from the second link provided.
"Why does the 8:1 rule matter? If the source output impedance is more than 1/8 of the headphone impedance, you’ll get distortion in the form of audible variation in the frequency response. Highs, lows, or mids may get extra emphasis. These variations in frequency response can range from subtle to easily audible, and often unpredictable."