Steve, I've used just 1 template, but you really need to pull hard and be very steady. Getting into the right stance/posture/position is important.
I'm no expert at hot wiring low aspect deltas [done 2] but I would think a template at the tip will help. You are learning to hot wire the most difficult type of tapered wing.
Make sure your pivot point is perfectly adjusted height-wise. I use a 10-32 screw, nuts and fender washer to make that happen. All foam needs to be measured for the exact thickness/centerline.
Don't expect to hit a homerun your first time up...learn from your errors and keep trying. Always place a board or something flat to secure the foam blank before you start cutting.
I usually place my free hand on the foam blank. Have fun!