another +1 on the heavier grind
Good prep + good technique and even the flexi full hollow till mow with authority.
But if you've never tried a heavier grind its well worth the effort. At least 1/3 of my rotation is 1/4 grind or heavier. I love them even though I love my flexi hollow. If anything gives me questions about a particular shave, the 1/4 grind is the go-to blade. I also find the taller blade makes it easier in tough growth.
'No disrespect whatsoever to those loving the vocal full or extra hollows. I love mine also, and can use them for any condition, thanks to the help I got here. I just have more enjoyment w/ the heavy grind for now.
A word on technique. Having struggled w/ the same issue, I found the most difficult condition I encountered was with a straight long blade (no smile), flexible hollow, where it engaged the full length of the heavy growth. A couple things helped. Beginning at the sideburn, where the grow is too narrow to load the entire length of the blade, I'd initiate fairly short strokes - sometimes only 1/16 - 1/8". Going south, as the grow widens on the cheek, I would angle the blade vertically so that only a portion of the blade was engaging the heavy growth. This kept issues with flex to a minimum and can be used all the way down & over the jaw line.
Another thing about the blade - you may find blades with a slight smile to be more smooth gliding. The smile can be so minute that a casual glance at the edge would not register the curvature. The 'shaving made easy' pdf that Jimmyhad often recommends, speaks not so directly about the smile, but about the frowning blade. It's unavoidable that if a frown prompts complaints from customers about 'pulling', the smile would be less likely to pull. If you see a heavy grind with a smile, you might want to give it a try. I have premium blades that are heavy w/ varying degrees of smile, but I also found a 5/8 Joseph Allen & Sons non-xxl at an antique show for $15 that stand proud against any blade I've tried.