Apologies for the confusion.
Many of our markets such as these popular GBP and JPY markets are setup tor Step Margin, which is banded depending upon position size. This means it is the StepMargin part of the ApiMarketInformationDTO that should be examined for the Margin information. The response looks similar to the screenshot below, which mirrors how it is shown on the Web platform.
After some more testing today, I suspect you are correct - I have placed a few successful orders with wider TriggerPrice targets.
I actually do have this process automated. My code that places orders receives the latest prices from Lightstreamer just before calling /order/newstoplimitorder. However, when dealing with distances that small, it seems likely that the market will occasionally move within your target distance.
I've built in a few other checks for this eventuality, as well as some TriggerPrice modifications and retries, should the first order attempt fail for that reason.
Thank you again for all your help!