I use dual wave much more than square wave, but to do the same thing.
If I’m below a 5 before the meal, I use dual wave to take some insulin 15 mins (approx 20%) before I eat and then spread the rest over the following 30mins. This stops me going hypo before the food kicks in, without waiting til I’ve finished eating to inject it all and then going high.
Large meals – over about 60g carbs I would do a dual wave. If I did square wave over an hour I’d be high as I wouldn’t have enough insulin in early enough. I’d generally do 50% of the insulin up front, then 50% over the next hour for something like pasta (those timings assume you start the bolus about 20mins before you start eating, so the last of the insulin goes in 40mins after you started eating). For pizza, I do 40% upfront and 60% over 2 hours.