With your achievements so far, every head turns to you to suggest a way to accomplish this.
I think it's important to remember that we are
suggesting a plan. If we suggest a plan that the others think is bad, it's not going to happen.
Plan Burning Shadows relies entirely on Mathilde's ability to scale a mere Moderately Complicated spell to full Battle Magic level. She's never cast a single Battle Magic spell before
in her life. I agree that the imagery would be really metal, but to everyone else sitting at the table it sounds incredibly egotistical and risky. Remember: Kragg the Grim is sitting right next to us. Do you believe that Kragg will approve of this plan?
There are alternatives to the leading plan if you think the KISS of normal fire won't work. Plan Go Commando, for example, surveys the entrance from Grobitown to the Citadel so that our engineers can direct us where to set charges and collapse the entrance.
Edit: I guess I should put a copy of my second favorite choice here, even if I'm not voting for it.
[] Plan Go Commando
-[] Survey and MAP the entrance from Grobitown to the Citadel, use this to generate a better set of charges to collapse it.
-[] sneak back up to gate, plant charges, blow it up. Rangers are infiltrating to Caldera rim to overlook passage, lotus poison bolts to provide a backup plan.
--[] if the explosion works, well, actually we're good to go. Roll up artillery to dominate the passage as the battle is underway, to further dissuade approach to the Citadel. If it's been less successful, adapt, but focus our subsequent efforts on dissuading entry to the Citadel.