Wyeast 1728 and apparent attenuation

Just too a sample of a wee heavy, with an OG of1.085 multiple readings. After 9 days of fermentation it is at 1.012@ 67f. Ferm temps started at 63f and at one week bumped up 2f each day.

Flavor and aroma is what is expected but the gravity reading seems too low for this yeast. I did pitch a very healthy 2L starter and within 6 hrs fermentation started.

My sample was taken from the top 2-3 inches of bucket. Could that cause misreading?

That's pretty high attenuation for that strain (typically 73-77% AA). You're sitting about 10% higher than average. I have noticed higher attenuation on multiple re-generations with this strain, and will typically get higher attenuation with large starters and yeastcakes. These factors coupled with a low mash temperature (what was your mash temp?) and well-managed fermentation temp schedule could push the AA a bit higher than manufacturers suggested range. I would say that if the flavor and aroma is what you expected then you're good. I wouldn't expect a shallow sample to cause an off reading, but you can certainly take another reading at bottling time to compare.

Mash temp was 156f @60min. The grain bill was 15lbs 2row and. 5lb roasted barley. Mash vol 5gals, and batch sparge with 5g with 175f water. I collected a total of 8.8g water and boiled for 3hrs down to 5.25g. Cooled wort and refractometer showed 1.92. I then added my 2l starter, OG down to 1.085 for total volume 5.75g.

I could have boiled for another 30min to lower volume.

.5 lb roasted barley...total 15.5lbs.