I'm thinking more of a triceratops design - still with the the wide crest to protect warriors, but also more combat utility. Shouldn't drop much, if any, protective ability.
If they can work out we've purposely designed the chargers, then they'll know we're sentient. They'll have much greater cause to aware for future tricks and traps, and also - most critically - denying knowledge to us. If they put trackers on each of their soldiers, then recover or destroy any bodies we attempt to take, that's an effective way of denying us information. If we're still just insects, they'll have no cause to. If they put locks on their weaponry, they'll be useless to us in the future, as we won't (possibly ever) have the tech to unlock them.
If we can breed tanks, we could breed flyers, so they could set up their turrets for AA beforehand; we could breed a better digger to undermine their defences, so they could sink seismic sensors to watch for it; they'll start preparing for what we might do, instead of what just we have done. It'll render any new surprises a lot less effective. Our warriors - and these new chargers - are, to a great extent, expendable to the extent we can lose more in the name of misinformation. Half of a war is information. At some point, we'd have to drop the masquerade, but by then we should hopefully have the upper hand.
That's why I want to risk using a slightly less effective design.