Iron spawning inside walls

playing solo on a private server

for the past week i have been searching for iron in the mine lvl 10-20. i have cleared these levels multiple times and have found iron node clusters only 4 times. 3 of those 4 times i almost missed it because 2 of the three nodes in the cluster were deep in the wall. I was still able to hit them all with my pick but the 2 nodes stuffed in the wall dropped all their ore behind the wall. Seems like its happening most of the time. i suppose its possible more are spawning completely behind the wall since there have been only 4 clusters within that range. are we meant to get most iron from turabada kills, or does iron spawn more frequently on deeper levels?