Here you see why I only use a half Presto Log at a time;
View attachment 221730
They expand!
So, I get the fire going with paper and kindling and then a couple of splits then when a nice coal bed happens I start with the Pres-To-logs a half log at a time.
Yes, that is a symptom of a lower compression vs the very dense extruded logs. They also leave more ash.
Even the NIEL's will do this if they pick up moisture, particularly on the ends. But, nothing like that!