When I set my stanza to Choice only it tells me the 1M spam message.
So I think that I am close.
1meter message actually means, that you are standing on the deposit area. it does not mean you close to what you looking for (choice in this case).
well, sometime it does lead you to kind of exact spot. and thats the fun part, personal experience (and not just some silly game mechanics) are playing big part.
I cast my prospect in a full circle ( upwards of 12 times to complete the circle ) and then when it tells me there is no materials , I back up to check the spot that I am standing on.
bad luck

i usually, mark nodes in new area by poping few sources without filter, then foraging one mat (to get focus back when source dies), and then spamming my filter prospecting to pop all nodes it can find. then running to node, and putting flag on my map.
ofcourse, i have 3 sec prospect
Thereby fully covering the entire area up to 5M away. And every time getting the message telling me nothing is there.
to cover 5m area you need "bit" more than 12 prospects. it does not take exact spot to pop node, but the more materials in area, the harder it is to pop node.
basicly server randomly selects location in your prospecting arc (5m/20degree for example), then checks if there is source, if there is, then it compares it to your filter, if there isn't, then it checks a bit around that spot.
now, when it does not find any node, it tells "no materials". if there is node, but you filter is blocking it, then "different kind mats present".
(exact logic on pop or error depends server code which i dont have access

, so just speculations)
just mark that spot as "hard to pop" and move on
ofcourse, they could change it so it selects all sources based your filter from your prospecting arc and pops randomly sources from it, but imho it would make prospecting bit to easy and not a challenge.