Baltic is considerably more resistant than basswood. Oak is more similar and I have 137/full for solid 1/4" oak. At the least I would run tests as laid out here…
Having your lenses, etc. clean is very important as well as using Set Focus.
I have cut a lot of 1/4"- 7/16" and you are definitely pushing the max thickness, so everything has to be right.
This was near 5/16" material…
Hmm i wonder if set focus would do the trick. Does the laser not automatically set the focus?? Ive been using the thick draftboard settings, but I thought it focuses before cutting.
Where the machine automatically does a set focus it could even be an empty place and be very wrong, but if the focus is other than perfect it will be wider and more burnt than otherwise.