I don't claim to know "how", but my 7 lb Benelli M-1's certainly have less felt recoil than my 7.5 lb fixed breach 870's. And these are the older M-1's without the benefit of of the comfortech stock and recoil pad.
Do they recoil more than my older 8.5 lb gas operated 11-87? Yes, but that is a fair compromise for a 1.5 lb lighter gun that has proven to make a higher percentage of hits for me. It does have a "tiny" bit more recoil than a gas gun, but significanlty less than any fixed breach gun of the same weight.
When you also consider the far simpler design and better reliability I'm sold on the Benelli's. I've owned Remingtons and Berettas as well as a try with the Mossbeerg 9200. The 9200 was a joke and why I'm hesitant to recommend the newer 930. The Beretta was a fine gun, but I just like the Benelli so much better. If I shot 10,000 rounds a year in competition I'd take the small recoil reduction of the Beretta, but with the amount of shooting I do recoil is simply not an issue. The Remington is not a bad gun, but has some features just do not like.