It's a balancing act between the gap & the spring tension. Both effect each other to some extent thats why the manuals make such a big deal about just
touching the barrel when gapping it. Some shoters of DWs even play with the spring tension fo "that little bit extra" even
It could be other things as well, but not having examined it myself I have no way of knowing.
Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”