I thought I'd better warn people that the adjacency bonus is only profitable it certain circumstances and one of those circumstances is high ore price.
My experience is limited but what I have been able to do so far:
The total amount of ore in a hex seems to depend on the tier of the ore, so on a planet like Maddis we might have total ore of around 500 to 550 mostly T1
On Ion and Symeon where I have done about 130 scans the total ore count is more like 270. For example my best he