Sounds like you're in a similar place to me. My neck stubble is getting marginally better each shave, but still not as close as the rest of my face, I just keep tentatively trying slightly different angles each shave & the goods ones stick, don't force it though or you'll just end up nicking yourself. There's no rush & no shame in finishing off with the mach 3, I still have to do it now & then, usually half an hour after I've shaved I'll rub my hand across my face & notice a bit I missed that I didn't see at the time, even this is getting less & less though.

The last revelation I had was probably 5 or 6 shaves back - the pressure I'm using is getting less & less as the shaves get better. It was initially very hard to do that with the chin area but it is the way you'll master it. Just keep going at it & you'll just get better & better over time & then suddenly it'll click.

I like that is says I'm now a senior member, I'm certainly no senior shaver - far far from it.