When placing trade posts, the rules state there must be 1 blank space between tradeposts. But you may put your tradepost adjacent to a settlement tile (assuming it is on a plains space)?
What you say is definitely correct under the Rules.
But it does seem to be silly that the Rules let you have your Workshop right next to a settlement, but then you have to build a round-about road in order to sell into it. This anomaly has led to our adopting a rule that your Workshop must be at least one space away from a settlement (as well as from other Workshops) - and, interestingly, the review of La Strada on RPG.Net by Shannon Appelcline indicates that that was what the game's designer intended.
Also, it sounds like some think the start player has an advantage, so has anyone tried reverse turn order for placing tradeposts? Just a thought.
As I've mentioned in another post,
in order to mitigate the advantage the first player has in choosing the 'best' site for their workshop, my wife and I now play that workshops have to be placed before the settlement counters are flipped to reveal whether they are cities or hamlets etc. We find that works fine, without having to resort to 'turn order reversal' or 'extra resources' supplementary remedial rules.