How to prioritize poke balls?

[ghost]

Expected Behavior

When catching low priority pokemons, the bot should use poke ball instead of great ball.
From the log, we can see that the pokemon caught is later exchanged. That mean is not better than the ones I already have. I list 2 instances here.

Actual Behavior

instance #1
[02:12:24] A wild Pidgey appeared! [CP 394] [Potential 0.38] [A/D/S 3/14/0]
[02:12:27] Used Greatball, with chance 41.36 (29 left)
[02:12:27] Captured Pidgey! [CP 394] [Potential 0.38] [3/14/0] [+210 exp]
[02:12:27] You now have 8 Pidgey candy!
...
[02:12:34] Keeping best 1 Pidgey, based on iv
[02:12:34] Exchanged Pidgey [CP 394] [IV 0.38] for candy.

instance No. 2
[03:14:29] A wild Fearow appeared! [CP 659] [Potential 0.67] [A/D/S 13/15/2]
[03:14:31] Catch rate of 23.02 with Greatball is low. Throwing Razz Berry (have 40)
[03:14:31] Threw a Razz Berry! Catch rate with Greatball is now: 23.02
[03:14:32] Used Greatball, with chance 34.53 (28 left)
[03:14:32] Fearow capture failed.. trying again!
[03:14:33] Catch rate of 34.53 with Greatball is low. Throwing Razz Berry (have 39)
[03:14:34] Threw a Razz Berry! Catch rate with Greatball is now: 34.53
[03:14:34] Used Greatball, with chance 51.79 (27 left)
[03:14:34] Captured Fearow! [CP 659] [Potential 0.67] [13/15/2] [+210 exp]
[03:14:34] You now have 99 Spearow candy!
[03:14:39] Moving towards pokestop Ukrainian Orthodox Cathedral - 0.05km
[03:14:41] Keeping best 1 Fearow, based on iv
[03:14:41] Exchanged Fearow [CP 659] [IV 0.67] for candy.

Your config.json (remove your credentials and any other private info)

    "evolve_captured":  "Caterpie, Pidgey, Weedle",
...
    "catch": {
        "any": {
            "catch_above_cp":   0,
            "catch_above_iv":   0,
            "logic":        "or"
        }
    },
    "release": {
        "any": {
            "release_below_cp": 0,
            "release_below_iv": 0,
            "logic":        "or"
        },
...
    "Pidgey":   { "keep_best_iv":    1 },

and Pidgey is not in the VIP list. The above are the 2 instances where Pidgey appears in my config file.
OS: Windows 10.

[ghost]

The usage of Pokeballs is calculated on the chance to catch the Pokemon is lower than 35% it will use a better ball. In your example the Pidgey has an CP which is to high for a normal Pokeball.

[ghost]

@extink Thank you for answering that. Now I understand.