You would have to explain better, but I am more than willing to help. I am fighting with my girlfriend, so if this is fragmented, apologies..... Best example is this:
Those chest divets (the Y's) are cut in initialy. But now look above the 'Y' cut. The easy way to make that is to burn out (iron or otherwise) the outline. What is better is to use 2mm craft foam over the top to define the details. HALO stuff defines it really well when it comes to panel line and steps, but here is my unwritten (and have not done it in a while) rule:
1) start straight in foam, keep your work as clean as you can.
2) Deep panel lines, solder iron tip, use a straight edge and define them with sharp corners.
3) Raised panels, trim craft foam (Michaels or otherwise) and set it in place until it looks right. SPRAY ADHESIVE! I don't care what you did before, spray and stick it.
4) You can definitely solder iron details over this now, but think about it before you do. I use craft adhesive on those next layers because I know I can tear that off if I need to.
5) Seal. Pick your way. I would douse with PVA, but it's pretty amazing how kind Plastidip is.
Point is, you can layer with craft foam.... You can burn in, you can layer, but what will work out is making depth using either. Stupid analogy, but pretend you are building a cake. Frosting is the last thing. If it looks close before frosting but not so much, fix it. If you don't think you know how, finish it, and the frosting will come. Frosting makes ugly cakes look amazing every day. And think about this; There are pros with ugly cakes who win awards.... just saying