[Bicorn]

I always found it a little weird that Basic has rules for increasing effective SM for thick objects (+2 for box/sphere, +1 for elongated box) but nothing for the opposite. -2 for a long thin object feels like a good houserule of thumb.
(Also I've never liked any of the mechanics that try to match hp with mass. I find the system works better when the mechanics based on abstracted characteristics and the ones based on real-world measurements are kept largely separate.)