Let's try a different approach...
Summon Negators do not have the same timing as cards that respond to summons ("Torrential Tribute", "Bottomless Trap Hole", etc...).
Summon Negators are activated before the monster is considered to be successfully summoned to the field.
Cards like "Torrential Tribute" are activated after the monster is considered to be successfully summoned to the field.
The mechanics of summoning a monster..101
1. First you announce your summon (Normal or Tribute).
2. Then, you place the monster on the field in face-up attack position.
If the summon is a Tribute Summon, you place the tributed monster in the Graveyard at this time. Any triggered effects of the tributed monster will trigger at this time, but will not activate until the Summon is considered to be successful or negated.
Even though the monster is physically on the field, it has not been successfully summoned at this time and is not considered to be 'on the field' yet.
This is why the continuous effects of monsters like "Jinzo" are not active yet.
3. You, as the Turn Player, have Priority to negate the summon of the monster first. If you choose to do so, this begins a chain.
UDE FAQ for "Forced Back" said:
You can activate "Forced Back" when you Normal or Flip Summon your own monster. You should announce this immediately after your Summon. Once you allow your opponent to activate "Torrential Tribute" you are acknowledging that the Summon was successful and you cannot activate "Forced Back".
If you do not wish to negate your summon, then your opponent has the chance to negate the summon. If they do so, this begins a chain.
4. If the summon is negated, then the monster is never considered to have made it to the field. Skip to step 6.
UDE FAQ for "Sangan" said:
If the Summon of this card is negated with "Horn of Heaven" or "Solemn Judgment" you do not get its effect.
UDE FAQ for "Witch of the Black Forest" said:
If the Summon of this card is negated with "Horn of Heaven" or "Solemn Judgment" you do not get its effect.
The monster is also not considered to be in your hand.
UDE FAQ for "Electric Snake" said:
If the summoning of "Electric Snake" is negated by "Solemn Judgment", etc. its effect is not activated, as it is not considered to have gone directly from your hand to the Graveyard.
UDE FAQ for "Minar" said:
If the summoning of "Minar" is negated by "Solemn Judgment", etc. its effect is not activated, as it is not considered to have gone directly from your hand to the Graveyard.
Since the monster is not considered to be on the field, nor in the hand, it is said to be in a 'limbo' state between the Hand and Field. (No 'limbo' is not any kind of official term. It was the best thing we came up with to explain where the monster was.)
5. If neither of you wish to negate the summon, then that monster is considered to have been successfully summoned to the field.
6. Any waiting Trigger effects from a monster that was offered as a tribute are activated now ("Sangan", "Witch of the Black Forest", etc..). If the monster was successfully summoned, any new triggers that activate in response to a monster being summoned (Monarchs, "Stumbling", etc...) will be added to the chain on top of the tributed monster's effect(s). NOW is when you can respond to a successful summon with cards like "Torrential Tribute", "Bottomless Trap Hole", etc..
So, as you can see, the timing for the cards is very different.
To address the issue of a monster being Flip Summoned. The act of Flip Summoning a monster places that monster into that 'limbo' zone because the Flip Summon can be negated just like any other summon. If the Flip Summon is negated, then that monster is not considered to have been on the field, even though that's where it started.
UDE FAQ from "Forced Back" said:
If you negate the Normal or Flip Summon of "Dark Magician of Chaos" with "Forced Back", it is returned to the hand and is not removed from play.
If "DMoC" was considered to have been on the field when Flip Summoned, then he would have been removed from play instead of being returned to the Hand.
Another way of looking at this would be from a targeting perspective.
Cards can only be targeted if they are in a public zone. What are the public zones? Field, Graveyard and RFP.
If an effect would affect a card in a non-public zone, it cannot target the card it would affect.
As we've seen from the ruings I provided, a monster that had its summon negated (any summon) is not considered to be on the field, so it is not in a public zone.
Since "Forced Back" is a card that negates the summon of a monster, then it affects a card that is not in a public zone, so it cannot target that card.
I hope this helps to better explain why "Forced Back" does not target.
And my apologies to all for my now removed outburst earlier. I took things personally which I should not have done.