The tendency will be to melt out the area by the wing tip. Deltas are difficult, but they are doable. A low aspect delta needs the temp set as low as possible. The panel can come out bowed from leading the wire through the foam before the lagging wire middle of the wing panel catches up.
Some melt out is workable/usable, but bowed panels from sag in the wire are useless junk.
I've been cutting from a pivot point for 25 years, the guy who taught me had been doing it since foam was first introduced as THE WAY to build control line combat planes in bulk.
The quality of your work will only be as good as your templates and the accuracy of your set up....the hot wire does not lie....
I use a $7 light dimmer switch coming straight off of 115VAC and in 25 years I'm on my 2nd dimmer now. I'll bet I've cut 50 "finish grade" sets of wings by now.
I use .020" solid stainless wire, it takes about 6 to 8 feet of it between your alligator clip "electrodes" for the dimmer to control it....so for most set ups there is extra stainless cutting wire in the circuit that lays slack.
The pivot point is height adjustable and I Cclamp it to the work table where the imaginary "projected" lines of the wing's leading and trailing edges meet.
The "T"handle is a chunk of wood with a nail driven through the middle, then folded back to give the cutting wire something to tie to.
The formica templates are sheet rock screwed to the foam. A little 3M77 helps, too.
You won't get shocked with this power source, not even a tingle..just make sure you are controlling the "HOT" with the dimmer and not the nuetral. Always wear shoes, too......