I've never done it myself. But from what I've heared it's bigger chip = faster skills. I can't tell you if bigger chip = cheaper skills, though (probably not).
from my 2 tests (one below 1k bio, one now at 1400) the minor heal is better in skill gain per ped than the med heal (which has the same decay but uses 1 more ME)
since i looted a powerful heal chip back in the days which i try to unlock atm, i will do this experiment again, but for now i am pretty sure that the minor heal has the best skill per ped rate
i wouldn't be surprised if the skill gain per time is better as well (since you have to heal more for the same heal, more chances for skill gain)
although, that i didn't test, since my approach to skill isn't about time, more about skill per ped
hence
Ehm, I asked what action I should perform in game, to achieve most biotropy skill, without wasting too much peds..
if my guess is right, you skilled melee a bit, so you already got bravado
consider to get, depending on your finances and healing tactics a minor heal (or bigger) to heal yourself after a fight
at least that would save fap cost (since i don't know what you hunt, armor cost as well maybe if the mob is low enough or you go down to a lower armor to have more need for heal)
see it that way, when you heal sweaters at Swamp Camp or Nea's, you save nothing at all
(sounds a bit harsh though, but when you got enough of them jumping up and down infront of you, pushing others away to be healed first and then shouting "HEAL!11!!" or so, you lose patience overtime)
Skill gain is related to ped burn. So you buy the most ped-burning/sec chip you can.
problem here is that the ME doesn't count as ped burned, just the tt of the "ammo"
an ex disciple of mine got from lvl pretty much 1 to ~8 now in say 2 weeks
and he didn't heal that long at swamp camp
my approach with healing myself is far slower #D
anyway, the chipping or natural question is such a thing
yes, you get side skills, but do you need those?
interesting one is courage
bravado for melee ppl, but generally a quite useless skill for all others
concentration is interesting, and it might even rise to an amount you can chip out later to sell (if you want to sell your bio and leave MF after that anyway)
Psyche can't be chipped, but has at least a (very) small effect on HP if i am not mistaken
besides, for the records
i am now at 1400 pts in bio, around lvl 13 biotropian (i skilled melee, so i back it up with some skills there, also sweated a lot) and have ~1100 conc
and around 800-900 came from sweating (SG skill 2400) ^^
anyway, hf
