Maybe the best solution is having NL1 a 12 team competition to mirror and align with the NPL.

Still retain promotion /relegation playoff game, but just 1 game.
But add a Final series to NL1

Week 1
1st are promoted and have week off in final series.
2nd have week off from final series but play a play off with 11th in NPL for a spot in following season's NPL. 1 game , winner takes all. Game at a Neutral venue

3 v 6
4 v 5

Week 2
1st play at home to lowest rank winner from previous weeks finals.

2nd play at home to highest rank winner from previous weeks finals.

Week 3
Grand Final at Neutral venue

NL1 gets 4 more regular season games, which is probably the right number. Opens up more spots in the pyramid for zone league teams in each division.