You don't need worry to start reducing risk. Any smart investor will lower risk as much as they can. If they're worried about their total investments, they would simply offer more (the same) investment as before.
If they're lowering amount/group in favor of number of groups, it probably means it makes more financial feasibility to do so.
Edit: Also realize that the initial investment also acts as a doorway for them to enter future larger deals, if they so wish. Shifting from a 75k investment to a 50k investment means they increase their opportunity without really sacrificing good will on the founders' part.
