I usually start long rides with HR cap (Z1-Z2), not IF and later go by RPE when HR becomes suppressed (night cold, fatigue, etc).
When looking power after the ride, it typically falls within 55-63% of FTP.
I am mostly riding in flat region, for me cruising speed difference between IF 0.6 vs 0.7 is pretty small (a la 30km/h vs 32km/h). Because I am not racing, I don’t care about this.