I must be missing something. How can the neck go inside die and NOT full length neck size AND STILL yet bump back shoulder?
You didn't state what caliber you're loading for. Here's some measurements from my 308 Win. and below, I have some from my 223 Remington.
I also use the Sinclair bump inserts. Fired cases come out of a couple of my rifles between 1.564"-68" on the gaugein the 308 Win. I bump them back to 1.562"-63". A SAAMI 1.630" 308 Winchester GO gauge measures 1.561" in my Sinclair bump gauge. My measurements are set with my digital caliper zeroed to "0.00" with the Sinclair gauge.
I have over 20 sets of rifle dies. I've never had a F/L die set 1/8" off of the shell holder and bump the shoulders back to minimum SAAMI specs. I also have a set of the Hornady bump gauges and I actually prefer the Hornady set since I seem to get better repeatable readings, but the Sinclair set works.
From your measurements, Are you reloading for the 223 Remington? The light just went on for me since you didn't say what caliber you're reloading.
I do have some measurements with the 223 Remington insert in my Sinclair gauge. Factory shoulders on several brands of Commercial and Military .223 and 5.56 NATO ammo measures 1.426"-27". Fired cases in a couple of my AR-15's measure 1.434"-1.437". I size the cases to 1.428"-30" to get them to chamber in the gas guns.
Do you have any factory or military loaded rounds you can measure?
Do you have a couple pieces of old brass you could sacrifice? Take the shoulder measurement, note it and then screw your F/L die down to the shell holder, F/L resize the brass and then measure the shoulder bump? I can't imagine you would be bumping back the shoulders to 1.400" more or less. Your die shouldn't be able to size the shoulder down to much less than 1.460 +or- a few thousandths.
You don't happen to have the decapping unit set too low do you? I have a set of Forster dies. Did you set the decapping stem up to the die directions? Forster dies have a different set up where the expander ball is set where it sits just below the case neck at the top of the up stroke. It is different than other dies. It does take a little fiddling with it to get it set up right.
I'm trying to help you figure this out. Your measurement are a bit different than mine, but if you could measure the shoulders on a couple of Factory loaded ammo, that would help you get into the ball park of what the minimum shoulder dimensions should be.