Just tried setting up the above-mentioned SOFTSTR3 in Petri-Foo manually. Note that you need to have X-Fade turned to 0, otherwise the end of the loop gets "eaten" by it and you won't be able to set the loop correctly.
That means that if you automatically read smp chunk, you need to adjust the amount of X-Fade or turn it completely off.
For example, say the end loop point is 210220 and whole file is 210300. If X-Fade is set to its default value of 100, then the farthest available loop point will be 210300-100=210200.
So we either just set X-Fade to 0 or else we can set it to 210300-210220=80.