The problem with that, is that adding a 'per grid' penalty requires cutting very deep into the pathing code, (I ran in that problem when I tried to implement an encumbrance system before) so instead I opted for a percent based approach, with a tweak: the percentage is rounded up to the next multiple of 50%, that has a result pretty similar to what you said (currently its equivalent to: unwounded = 2, wounded = 3, severely wounded = 4, but doubling the penalty would have exactly the effect of your example) -- with straight standing moves that is, diagonals and crawling are not so simple due to rounding errors... maybe I could revisit the problem...
That sounds good, too. If possible, can we make it always round to an integer for each tile? I just want to avoid something where moving 1 tile = 2 TU and moving 2 tile = 5 TU because behind the scenes one tile = 2.4, so two tiles = 4.8. In other words, it should scale from 1 tile to several in a way that is clear to the player.
Since the spec calls for increasing the TU cost for shooting I simply add a penalty of 1 to 5 TU depending on the severity of wounds, I tried a percent based penalty but I felt it was too harsh on the more expensive firemodes -- and since the reaction penalty affects the cost of reaction fire shoots it suffered of the same problem, so I took the same approach for both, but maybe I was just ramping the penalties too high...
I know this just a first-pass and values can be adjusted, but I would recommend a higher penalty. Keep in mind that healing with the medikit costs 20 TU, so the trade-off of using one soldier's entire turn just to avoid a 1-5 TU penalty when firing is not great. You're right, though. With higher penalties wounds will be a big deal for high-TU firemodes, making some weapons virtually unusable (sniper rifles, rocket launcher). I'm not sure that's such a bad thing -- it will effect aimed sniper firemodes, full-auto machine gun, rocket launcher, etc. All of these are firemodes that would be very difficult to do well if wounded.
With a percentage mode, it would mean that a pistol is still able to fire without a great TU penalty, which might be a nice benefit to taking and using low-TU firemodes. But it will introduce irregularities -- like why a wounded soldier should be able to fire a powerful shotgun with little penalty. I could go either way on this.
* Random, overcomplicated idea: might be cool if weapons had a "handling" parameter, that effected reaction fire, wound penalty, etc for difficult to handle weapons. *
Based on soldier's max HP, thought I'd make more sense, specially since aliens can be wounded too, I assumed that sturdier creatures (lots of HP) would be more resistant to wounds.
Sounds good.