It sounds like the values being returned are text values rather than numbers. If they are text values then, as you say, the 1 in 16 will be used and evaluated against 4, also MIN(A1,B1) will give 0
If you enclose your original INDEX/MATCH formula in a VALUE function, e.g.
=VALUE(INDEX(A1:A10,MATCH(C1,B1:B10,0)))
then that should return a number as required
Alternatively use
=A1+0>B1+0
or
=MIN(A1+0,B1+0)
regards, barry